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1.
C. E. Crocker J. J. Cech Jr. 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(1):50-60
The effect of environmental hypercapnia on respiratory and acid-base variables was studied in white sturgeon, Acipenser transmontanus. Blood PCO2, PO2, pH, hemoglobin concentration, and plasma lactate, glucose, catecholamines and cortisol were measured first under normocapnia
(water PCO2 < 0.5 Torr, 1 Torr = 133.32 Pa), then under hypercapnia (25–35 Torr) and a final return to normocapnia at 19 ± 0.5 °C. Acute
(≤ 2h) hypercapnia significantly increased arterial PCO2 (8-fold increase), ventilation frequency (2-fold increase), plasma HCO3
− (2.3-fold) and decreased arterial pH (to 7.15 ± 0.02). After 24 h, norepinephrine, epinephrine and cortisol, were significantly
increased, and arterial pH reached its nadir (7.10 ± 0.03). During the 72- and 96-h-periods, arterial PCO2 (24 ± 4.4 Torr) and ventilatory frequency (105 ± 5 breaths min−1) stabilized, HCO3
− reached its apparent maximum (23.6 ± 0.0 mmol−1), glucose decreased by 32%, and pH increased significantly to 7.31 + 0.03. The return to normocapnia completely restored
arterial PCO2 (2.5 ± 0.14 Torr), HCO3
− (7.4 ± 0.59 mmol · l−1), ventilation frequency (71 ± 7 breaths · min−1), and pH (7.75 ± 0.04). Overall, hypercapnia produced a respiratory acidosis, hyperventilation, a transient norepinephrine
“spike”, and increased plasma catecholamines, cortisol, and arterial PO2. The respiratory acidosis was only partially compensated (35% pH restoration) 96 h after the onset of hypercapnia and resulted
in a significantly decreased blood-O2 affinity (Bohr effect), as determined by construction of in vitro blood O2 equilibrium curves at 15 °C and 20 °C. Prolonged exposure to hypercapnia may lead to acid-base disturbances and negatively
affect growth of white sturgeon.
Accepted: 17 August 1997 相似文献
2.
Jensen FB Koldkjaer P Bach A 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(7):489-495
Nitrite influx into crayfish showed saturation kinetics, supporting a carrier-mediated uptake. Addition of 4,4′-diisothiocyanatostilbene-2,2′-disulfonate
(DIDS: at 10−5, 10−4 and 10−3 M) and bumetanide (at 10−5 M and 10−4 M) to the ambient water did not significantly affect nitrite influx. Rather than suggesting that neither Cl−/HCO3
− exchange nor K+/Na+/2Cl− cotransport were involved in the transport, this may reflect that the gill cuticle has a low permeability to the pharmacological
agents, or that the sensitivity of the transport mechanism to the inhibitors is low. Nitrite accumulation in the haemolymph
was significantly decreased during hypercapnic conditions compared to normocapnic conditions. This supports the idea that
an acid–base regulatory decrease in Cl−(influx)/HCO3
− (efflux) induced by hypercapnia should decrease NO2
− uptake if NO2
− and Cl− share this uptake route. The respiratory acidosis caused by exposure to hypercapnia alone was partially compensated by HCO3
− accumulation in the haemolymph. Combined exposure to hypercapnia and nitrite improved pH recovery, mainly by augmenting the
[HCO3
−] increase, but also by decreasing haemolymph PCO2. Exposure to nitrite in normocapnic water induced an initial increase in haemolymph [HCO3
−] and later also a decrease in PCO2. Thus, the improved acid-base compensation during combined hypercapnia and nitrite exposure was an amplification of this
nitriteinduced response. Haemolymph base excess rose much more than haemolymph [Ca], suggesting that transfer of acid-base
equivalents between animal and water was more important than H+ buffering by exoskeletal CaCO3 in mediating the increase in haemolymph [HCO3
−].
Accepted: 27 June 2000 相似文献
3.
Wood CM Pärt P 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(3):175-184
The influence of a CO2/HCO−
3-buffered medium on intracellular pH regulation of gill pavement cells from freshwater rainbow trout was examined in monolayers
grown in primary culture on glass coverslips; intracellular pH (pHi) was monitored by continuous spectrofluorometric recording from cells loaded with 2′,7′-bis(2-carboxyethyl)-5(6)-carboxy-fluoroscein. When cells in HEPES-buffered medium at normal pH=7.70 were transferred to normal
CO2/HCO−
3-buffered medium {P
CO2=3.71 mmHg, [HCO−
3]= 6.1 mmol l−1, extracellular pH (pHe)=7.70}, they exhibited a brief acidosis but subsequently regulated the same pHi (∼7.41) as in HEPES. Buffer capacity (β)
increased by the expected amount (5.5–8.0 slykes) based on intracellular [HCO−
3], and was unaffected by most drugs and treatments. However, after transfer to high P
CO2=11.15 mmHg, [HCO−
3]= 18.2 mmol l−1 at the same pHe=7.70, the final regulated pHi was elevated (∼7.53). The rate of correction of alkalosis caused by washout of this high P
CO2, high-HCO−
3 medium was unaffected by removal of extracellular Cl−. Removal of extracellular Na+ lowered resting pHi and greatly inhibited the rate of pHi recovery from acidosis. Bafilomycin A1 (3 μmol l−1) had no effect on these responses. However amiloride (0.2 mmol l−1) inhibited recovery from acidosis caused by washout of an ammonia prepulse, but did not affect resting pHi, the latter differing from the response in HEPES where amiloride also lowered resting pHi. Similarly 4-acetamido-4′- isothiocyanatostilbene-2,2′-disulfonic acid, sodium salt (0.1 mmol l−1) did not affect resting pHi but slowed the rate of recovery from acidosis, though to a lesser extent than amiloride. Removal of extracellular Cl− also slowed the rate of recovery but greatly increased β by an unknown mechanism; when this was taken into account, H+ extrusion rate was unaffected. These results are consistent with the presence of Na+-(HCO−
3)N co-transport and/or Na+-dependent HCO−
3/Cl− exchange, in addition to Na+/H+ exchange, as mechanisms contributing to “housekeeping” pHi regulation in gill cells in CO2/HCO−
3 media, whereas only Na+/H+ exchange is seen in HEPES. Both Na+-independent Cl−/HCO−
3 exchange and V-type H+-ATPase mechanisms appear to be absent from these cells cultured in isotonic media.
Accepted: 30 November 1999 相似文献
4.
Steve F. Perry Marvin H. Braun Janet Genz Branka Vulesevic Josi Taylor Martin Grosell Kathleen M. Gilmour 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2010,180(8):1213-1225
The plainfin midshipman (Porichthys notatus) possesses an aglomerular kidney and like other marine teleosts, secretes base into the intestine to aid water absorption.
Each of these features could potentially influence acid–base regulation during respiratory acidosis either by facilitating
or constraining HCO3
− accumulation, respectively. Thus, in the present study, we evaluated the capacity of P. notatus to regulate blood acid–base status during exposure to increasing levels of hypercapnia (nominally 1–5% CO2). Fish exhibited a well-developed ability to increase plasma HCO3
− levels with values of 39.8 ± 2.8 mmol l−1 being achieved at the most severe stage of hypercapnic exposure (arterial blood PCO2 = 21.9 ± 1.7 mmHg). Consequently, blood pH, while lowered by 0.15 units (pH = 7.63 ± 0.06) during the final step of hypercapnia,
was regulated far above values predicted by chemical buffering (predicted pH = 7.0). The accumulation of plasma HCO3
− during hypercapnia was associated with marked increases in branchial net acid excretion (J
NETH+) owing exclusively to increases in the titratable alkalinity component; total ammonia excretion was actually reduced during
hypercapnia. The increase in J
NETH+ was accompanied by increases in branchial carbonic anhydrase (CA) enzymatic activity (2.8×) and CA protein levels (1.6×);
branchial Na+/K+-ATPase activity was unaffected. Rectal fluids sampled from control fish contained on average HCO3
− concentrations of 92.2 ± 4.8 mmol l−1. At the highest level of hypercapnia, rectal fluid HCO3
− levels were increased significantly to 141.8 ± 7.4 mmol l−1 but returned to control levels during post-hypercapnia recovery (96.0 ± 13.2 mmol l−1). Thus, the impressive accumulation of plasma HCO3
− to compensate for hypercapnic acidosis occurred against a backdrop of increasing intestinal HCO3
− excretion. Based on in vitro measurements of intestinal base secretion in Ussing chambers, it would appear that P. notatus did not respond by minimizing base loss during hypercapnia; the increases in base flux across the intestinal epithelium in
response to alterations in serosal HCO3
− concentration were similar in preparations obtained from control or hypercapnic fish. Fish returned to normocapnia developed
profound metabolic alkalosis owing to unusually slow clearance of the accumulated plasma HCO3
−. The apparent inability of P. notatus to effectively excrete HCO3
− following hypercapnia may reflect its aglomerular (i.e., non-filtering) kidney coupled with the normally low rates of urine
production in marine teleosts. 相似文献
5.
Haemolymph samples were withdrawn from routinely active male intermoult Glyptonotus held at 0 ± 0.5°C, and analysed for blood-gas and acid-base variables. In both the arterialised (a) and venous (v) haemolymph,
over 50% of the oxygen was transported as dissolved oxygen at PaO2 and PvO2 levels of 12.0 ± 1.15 and 7.70 ± 1.89 kPa, respectively. The maximum oxygen-carrying capacity of the haemocyanin (CmaxHcO2) was relatively low at 0.19 ± 0.05 mmol l−1, accompanied by relatively low protein and [Cu2+] levels indicating low circulating haemocyanin concentrations. Arterialised haemolymph had a mean pH of 7.88 ± 0.02(6) at
a PCO2 of 0.12 ± 0.01(6) kPa and a bicarbonate level of 12.95 ± 0.80(6) mequiv l−1 with small differences in PCO2 and pH between arterial and venous haemolymph. The non-bicarbonate buffering capacity of Glyptonotus haemolymph was low at −2.0 mequiv l−1 HCO3
− pH unit−1. Haemolymph [l-lactate] and [d-glucose] levels were similar at < 1 mmol l−1 in animals held in the laboratory and those sampled in Antarctica. The blood-gas and acid-base status of Glyptonotus haemolymph may be a reflection of the low and stable temperatures experienced by this Antarctic crustacean.
Received: 14 August 1996 / Accepted: 3 November 1996 相似文献
6.
Günzel D Galler S 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(7):523-529
The inhibitory motoneurons of crustaceans form synapses both with the sarcolemma of muscle fibres and with the very distal
branchings of the excitatory motoneurons. The transmitter of these synapses is GABA (γ-aminobutyric acid) which is known to
open Cl− channels. Studies on the dactyl opener muscle of crayfish suggest that application of GABA not only leads to an increase
in the Cl− permeability but also to a considerable HCO−
3 conductance that causes an intracellular acidification. To investigate possible physiological implications, we measured the
intracellular pH of various muscle fibre types of crayfish and crab using pH-sensitive microelectrodes. Independent of the
presence or absence of inhibitory innervation, bath application of 10−5 mol l−1 GABA led to acidification in all fibre types (pH change: 0.14 ± 0.08, n=11). In no preparation was a change in intracellular pH observed upon stimulation of specific or common inhibitory motoneurons
with 10–40 pulses s−1 for 2–5 min. The results suggest that HCO−
3 conductance cannot be activated through synaptic GABA receptors. However, all crustacean muscle fibre types seem to possess
extrasynaptic GABA-sensitive channels that exhibit a considerable HCO−
3 conductance. The physiological importance of these channels remains to be elucidated.
Accepted: 13 July 2000 相似文献
7.
Mechanisms of inorganic carbon assimilation were investigated in the deep-water alga Phyllariopsis purpurascens (C. Agardh) Henry et South (Laminariales, Phaeophyta). The gross photosynthetic rate as a function of external pH, at a constant
concentration of 2 mM dissolved inorganic carbon (DIC), decreased sharply from pH 7.0 to 9.0, and was not substantially different
from 0 above pH 9.0. These data indicate that P. purpurascens is inefficient in the use of external HCO3
− as a carbon source in photosynthesis. Moreover, the photosynthetic rate as a function of external DIC and the highest pH
(9.01 ± 0.07) that this species can achieve in a closed system were consistent with a low capacity to use HCO3
−, in comparison to many other species of seaweeds. The role of external carbonic anhydrase (CA; EC 4.2.1.1) on carbon uptake
was investigated by measuring both the HCO3
−-dependent O2 evolution and the CO2 uptake, at pH 5.5 and 8.0, and the rate of pH change in the external medium, in the presence of selected inhibitors of extra-
and intracellular CA. Photosynthetic DIC-dependent O2 evolution was higher at pH 5.5 (where CO2 is the predominant form of DIC) than at pH 8.0 (where the predominant chemical species is HCO3
−). Both intra- and extracellular CA activity was detected. Dextran-bound sulfonamide (DBS; a specific inhibitor of extracellular
CA) reduced the photosynthetic O2 evolution and CO2 uptake at pH 8.0, but there was no effect at pH 5.5. The pH-change rate of the medium, under saturating irradiance, was reduced
by DBS. Phyllariopsis purpurascens has a low efficiency in the use of HCO3
− as carbon source in photosynthesis; nevertheless, the ion can be used after dehydration, in the external medium, catalyzed
by extracellular CA. This mechanism could explain why the photosynthetic rate in situ was higher than that supported solely
by the diffusion of CO2 from seawater.
Received: 6 March 1998 / Accepted: 22 June 1998 相似文献
8.
Müller F Aschenbach JR Gäbel G 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(4):337-343
This study sought to investigate effects of short-chain fatty acids and CO2 on intracellular pH (pHi) and mechanisms that mediate pHi recovery from intracellular acidification in cultured ruminal epithelial cells of sheep. pHi was studied by spectrofluorometry using the pH-sensitive fluorescent indicator 2′,7′-bis (carboxyethyl)-5(6′)-carboxyfluorescein
acetoxymethyl ester (BCECF/AM). The resting pHi in N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid (HEPES)-buffered solution was 7.37 ± 0.03. In HEPES-buffered solution,
a NH4
+/NH3-prepulse (20 mM) or addition of butyrate (20 mM) led to a rapid intracellular acidification (P < 0.05). Addition of 5-(N-ethyl-N-isopropyl)-amiloride (EIPA; 10 μM) or HOE-694 (200 μM) inhibited pHi recovery from an NH4
+/NH3-induced acid load by 58% and 70%, respectively. pHi recovery from acidification by butyrate was reduced by 62% and 69% in the presence of EIPA (10 μM) and HOE-694 (200 μM),
respectively. Changing from HEPES- (20 mM) to CO2/HCO3
−-buffered (5%/20 mM) solution caused a rapid decrease of pHi (P < 0.01), followed by an effective counter-regulation. 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS; 100 μM) blocked
the pHi recovery by 88%. The results indicate that intracellular acidification by butyrate and CO2 is effectively counter-regulated by an Na+/H+ exchanger and by DIDS-sensitive, HCO3
−-dependent mechanism(s). Considering the large amount of intraruminal weak acids in vivo, both mechanisms are of major importance
for maintaining the pHi homeostasis of ruminal epithelial cells.
Accepted: 8 March 2000 相似文献
9.
Amin-Naves J Giusti H Hoffmann A Glass ML 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2007,177(5):529-534
Lungfish represent a probable sister group to the land vertebrates. Lungfish and tetrapods share features of respiratory control,
including central, peripheral and intrapulmonary CO2 receptors. We investigated whether or not central chemoreceptors in the lungfish, L. paradoxa, are stimulated by CO2 and/or pH. Ventilation was measured by pneumotachography for diving animals. The fourth cerebral ventricle was equipped with
two catheters for superfusion. Initially, two control groups were compared: (1) catheterized animals with no superfusion and
(2) animals superfused with mock CSF solutions at pH = 7.45; PCO2 = 21 mmHg. The two groups had virtually the same ventilation of about 40 ml BTPS kg−1 h−1 (P > 0.05). Next, PCO2 was increased from 21 to 42 mmHg, while pHCSF was kept at 7.45, which increased ventilation from 40 to 75 ml BTPS kg−1 h−1. Conversely, a decrease of pHCSF from 7.45 to 7.20 (PCO2 = 21 mmHg) increased ventilation to 111 ml BTPS kg−1 h−1. Further decreases of pHCSF had little effect on ventilation, and the combination of pHCSF = 7.10 and PCO2 = 42 mmHg reduced ventilation to 63 ml BTPS kg−1 h−1. 相似文献
10.
Protective effects of prostaglandins in the isolated gastric mucosa of the eel, Anguilla anguilla 总被引:1,自引:0,他引:1
Faggio C Denaro MG Lionetto MG Trischitta F 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(5-6):357-363
The protective effect of endogenous prostaglandins on the fish gastric mucosa was evaluated by studying the effect of indomethacin
and aspirin, known cyclooxigenase inhibitors, on the mucosal ulceration in the isolated gastric sacs of Anguilla anguilla. Gastric sacs devoid of muscle layers were incubated in the presence of indomethacin (10−4 mol · l−1) or aspirin (10−4 mol · l−1) in different experimental conditions. Both the anti-inflammatory drugs produced ulcers, but the effects were more severe
in the presence of histamine and in the absence of HCO3
− in the incubation bath. The effects of prostaglandin E2 (PGE2) on acid secretion rate (JH) and on alkaline secretion rate (JOH) were evaluated (with the aid of the pH stat method) in isolated gastric mucosa mounted in Ussing chambers. We found that
PGE2 (10−8–10−5 mol · l−1) increased JH in a dose-dependent manner. In tissues pretreated with luminal omeprazole (10−4 mol · l−1), PGE2 stimulated gastric alkaline secretion. It was nullified by serosal removal of HCO3
− or Na+ and by serosal ouabain (10−4 mol · l−1). These results suggested that prostaglandins also exert their protective effects in fish gastric mucosa. This protection
seems partially due to a stimulation of exogenous HCO3
− transport from the serosal to the mucosal side. It is likely that this transport is an active transcellular mechanism coupled
to Na+ transport.
Accepted: 14 April 2000 相似文献
11.
A mathematical model of the HCO−
3-secreting pancreatic ductal epithelium was developed using network thermodynamics. With a minimal set of assumptions, the
model accurately reproduced the experimentally measured membrane potentials, voltage divider ratio, transepithelial resistance
and short-circuit current of nonstimulated ducts that were microperfused and bathed with a CO2/HCO−
3-free, HEPES-buffered solution, and also the intracellular pH of duct cells bathed in a CO2/HCO−
3-buffered solution. The model also accurately simulated: (i) the effect of step changes in basolateral K+ concentration, and the effect of K+ channel blockers on basolateral membrane potential; (ii) the intracellular acidification caused by a Na+-free extracellular solution and the effect of amiloride on this acidification; and (iii) the intracellular alkalinization
caused by a Cl−-free extracellular solution and the effect of DIDS on this alkalinization. In addition, the model predicted that the luminal
Cl− conductance plays a key role in controlling both the HCO−
3 secretory rate and intracellular pH during HCO−
3 secretion. We believe that the model will be helpful in the analysis of experimental data and improve our understanding of
HCO−
3-transporting mechanisms in pancreatic duct cells.
Received: 18 October 1995/Revised: 5 July 1996 相似文献
12.
C. E. Crocker G. R. Ultsch D. C. Jackson 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(4-5):249-255
We examined changes in blood gases, plasma ions, and acid-base status during prolonged submergence (6 h) of four aquatic
turtle species in aerated water at 20 °C. Our objective was to determine whether the temperate species, Chrysemys picta bellii, exhibits greater tolerance to submergence apnea than the tropical species, Pelomedusa subrufa, Elseya novaeguineae, and Emydura subglobosa. Blood was sampled from indwelling arterial catheters for measurements of blood PO2, PCO2, pH, and hematocrit and for plasma concentrations of lactate, glucose, Na+, K+, Cl−, total Ca, and total Mg. The pattern of change was similar in all species: a combined respiratory and metabolic acidosis
associated with a marked decrease of blood PO2. The severity of the acidosis developed in the temperate species, however, was significantly less than that of the tropical
turtles. Lactate rose significantly and HCO3
− fell proportionately in all turtles; changes in other plasma ion concentrations were small but were generally in the directions
consistent with compensatory exchanges with other body compartments; i.e., cations (K+, Ca, and Mg increased) and anions (Cl− decreased). The results indicate that hypoxia tolerance is a conserved trait in turtles, even in those that do not experience
enforced winter submergence, and that the temperate species may be superior in this capacity because of reduced metabolic
rate.
Accepted: 3 March 1999 相似文献
13.
S. Morris J. Callaghan 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(5):377-388
The Australian Yabby, Cherax destructor, inhabits occasionally hypoxic water. The respiratory gas, acid-base, metabolite and energetic status of this crayfish was
assessed during progressive hypoxia and during 3 h at a water PO2 of 1.33 kPa. The O2 affinity of haemocyanin from C. destructor was increased by lactate (Δlog P
50/Δlog[lactate] = −0.111) and by Ca (Δlog P
50/Δlog[Ca] = −0.62) but not by urate. While the non-bicarbonate buffering capacity was low (Δ[HCO3
−]/ ΔpH=−4.89) the haemocyanin had a low sensitivity to pH changes (ϕ = −0.33). The crayfish showed a compensatory hyperventilation,
which induced a respiratory alkalosis, until the water O2 partial pressure declined below 2.67 kPa, after which the O2 uptake rate was approximately 10% of normoxic rates. The high haemocyanin-O2 affinity maintained haemolymph O2 content during progressive hypoxia despite the normally low arterial O2 partial pressure of C. destructor. During severe hypoxia, pH decreased but increased lactate aided in maintaining haemocyanin-O2 saturation. The importance of regulated haemocyanin-O2 affinity in hypoxic C. destructor was reduced by lowered metabolism, including reduced cardiac output, and the consequent reduction in O2 requirement. Anaerobiosis became important only at very low PO2 but thereafter proceeded rapidly, supported by a marked hyperglycaemia. There was no depletion of adenylates, even after
3 h of severe hypoxia. The tail muscle of C. destructor held small amounts of glycogen which would sustain anaerobiosis for a only a few hours. Hypometabolism seems an important
hypoxic response but severe hypoxia may encourage the crayfish to breathe air.
Accepted: 26 February 1998 相似文献
14.
Extracellular and intracellular acid-base balance is necessaryfor the maintenance of normal metabolic processes. The primarysource of acid is metabolically produced CO2, and the CO2/HCO3system is the most significant buffer. The regulation of acid-basebalance is complex, involving the interaction between respiratorygas exchange and ion transport. In aquatic crustaceans respirationis governed by the need to extract oxygen from water, an O2-poormedium; thus, acid-base balance is maintained primarily throughion transport mechanisms. These mechanisms include Na+/H+ andCl/HCO3 exchange processes that are sensitiveto the extracellular acid-base status of the animal. In marinecrabs, ion regulation and acid-base balance are accomplishedby the posterior gills, while in freshwater species all gillsand the antennal gland perform these functions. Intracellularacid-base balance appears to be maintained primarily by iontransport across the cell membrane. Hemolymph pH varies inverselywith acclimation temperature and salinity. In both cases Pco2remains nearly constant, and the pH change is a result of changesin hemolymph HCO3 concentrations brought about by ionexchange mechanisms. Environmental hypercapnia or hyperoxiainduces a repiratory acidosis characterized by increased Pco2,low pH, and elevated HCO3; this is partially compensatedfor by ion exchange processes that bring about a further increasein hemolymph HCO3. Exercise causes a mixed respiratoryand metabolic acidosis with compensation via H+ ion excretionand hyperventilation. 相似文献
15.
Harald Kosegarten Franz Grolig Andreas Esch Karl-Heinz Glüsenkamp Konrad Mengel 《Planta》1999,209(4):444-452
A fluorimetric ratio technique was elaborated to measure apoplastic pH in the outer root cortex of maize (Zea mays L.) grown hydroponically. A newly synthesized fluorescent probe, fluorescein boronic acid (pKa = 5.48), which covalently binds to the cell wall of the outer cell layers, was used. Under conditions of saturating ion concentrations
the apoplastic pH was determined along the root axis ranging from 1 to 30 mm behind the root tip. Apoplastic pH was recorded
for root segment areas (1 mm2), and pH values of high statistical significance were obtained. With an external solution of pH 5, the apoplastic pH was
about pH 5.1 in the division zone, between pH 4.8 and 4.9 in the elongation region and about pH 4.9 in the root hair zone.
At an external pH of 8.6, the difference between the external pH and the apoplastic pH was considerably more, with a pH of
5.2–5.3 in all root zones. Addition of 1 mM NH4
+ caused a small apoplastic pH decrease (0.05 of a pH unit) in all root zones. Apoplastic alkalization upon application of
6 mM NO3
− was highest (0.3 of a pH unit) in the zone where root hairs emerge; in the division and early elongation zones, apoplastic
pH increased only transiently. In the presence of 10 mM HCO3
−, NO3
− elicited a higher and persistent alkalization (0.06–0.25 of a pH unit) in all root zones. Application of fusicoccin reduced
apoplastic pH from 4.85 to 4.75 in the elongation zone, while inhibition of the H+-ATPase with vanadate alkalized the apoplast in the root hair zone from pH 5.4 to 5.6. The observed pH differences along the
root axis upon differential N supply and application of HCO3
− provide evidence that this new pH technique is a useful tool with which to measure apoplastic pH, and in future may permit
measurements at microsites at the cell level by use of microscope imaging.
Received: 26 August 1998 / Accepted: 4 May 1999 相似文献
16.
Carlos E. Crocker Daniel F. Stiffler 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1991,161(5):460-464
Summary The responses of net and unidirectional fluxes of Na+ and acid-base balance to the drug amiloride were assessed during normocapnia and hypercapnia in larval salamanders, Ambystoma tigrinum. Isotope flux measurements demonstrated that 10-4
M amiloride in the external medium inhibits Na+ influx during normocapnia and reverses the usual increase in influx of this ion during hypercapnia, causing a significant decrease instead. Measurements of blood-gas/acid-base balance conditions of artcrially cannulated salamanders demonstrated a significant metabolic acidosis in amiloridetreated animals that did not occur in untreated animals over the same period. the same concentration of amiloride also blocked the normal compensatory increase in [HCO
-
3
] that follows a respiratory acidosis produced by a hypercapnic environment.Abbreviations
IU
international nnits
-
J
in
influx
-
J
net
net flux
-
PCO
2
parial pressure of carbon dioxide 相似文献
17.
Roles of Volume-sensitive Cl<Superscript>−</Superscript> Channel in Cisplatin-induced Apoptosis in Human Epidermoid Cancer Cells 总被引:4,自引:0,他引:4
The anti-cancer drug cisplatin induces apoptosis by damaging DNA. Since a stilbene-derivative blocker of Cl−/HCO3− exchangers and Cl− channels, SITS, is known to induce cisplatin resistance in a manner independent of intracellular pH and extracellular HCO3−, we investigated the relation between cisplatin-induced apoptosis and Cl− channel activity in human adenocarcinoma KB cells. A stilbene derivative, DIDS, reduced cisplatin-induced caspase-3 activation
and cell death, which were detected over 18 h after treatment with cisplatin. DIDS was also found to reduce sensitivity of
KB cells to 5-day exposure to cisplatin. Whole-cell patch-clamp recordings showed that KB cells functionally express volume-sensitive
outwardly rectifying (VSOR) Cl− channels which are activated by osmotic cell swelling and sensitive to DIDS. Pretreatment of the cells with cisplatin for
12 h augmented the magnitude of VSOR Cl− current. Thus, it is concluded that cisplatin-induced cytotoxicity in KB cells is associated with augmented activity of a
DIDS-sensitive VSOR Cl− channel and that blockade of this channel is, at least in part, responsible for cisplatin resistance induced by a stilbene
derivative. 相似文献
18.
Mechanisms of inorganic carbon acquisition in Gracilaria gaditana nom. prov. (Rhodophyta) 总被引:1,自引:0,他引:1
The mechanisms for acquisition of dissolved inorganic carbon (DIC) in the red macroalga Gracilaria gaditana nom. prov. have been investigated. The capacity for HCO3
− use by an extracellular carbonic anhydrase (CA; EC 4.2.1.1), and by an anion exchanger with similar properties to that of
red blood cells (AE1), has been quantified. It was illustrated by comparing O2 evolution rates with those theoretically supported by CO2, as well as by photosynthesis-pH curves. Both external and internal CA, and a direct uptake were involved in HCO3
− use, since photosynthesis and pH evolution were affected by acetazolamide, 6-ethoxyzolamide (inhibitors of external and total
CA, respectively) and 4,4′-diisothiocyanatostilbene-2,2′-disulfonate, (DIDS; an inhibitor of HCO3
− exchanger protein). The activity of the external CA was detected by a potentiometric method and by an alternative method
based on the study of O2 evolution after addition of CO2 and acetazolamide. The latter method showed a residual photosynthetic rate due to direct HCO3
− use. Inhibitors caused a reduction in the pH compensation points in pH-drift experiments. The CO2 compensation points for photosynthesis increased when the inhibitors were applied, indicating a suppresion of the pathways
involved in the carbon-concentrating mechanism. The net photosynthesis rates as a function of DIC concentration displayed
a biphasic pattern that could be supported by the occurrence of the two mechanisms of HCO3
− use. The potential contribution to HCO3
− acquisition by the DIDS-sensitive mechanism was higher after culturing at a high pH. Our results suggest that the HCO3
− use by Gracilaria gaditana is carried out by the two DIC uptake mechanisms. These operate simultaneously with different affinities for DIC, the indirect
HCO3
− use by an external CA activity being the main pathway. The presence of a carbon-concentrating mechanism confers eco-physiological
advantages in a fluctuating ecosystem subjected daily to high pHs and low DIC concentrations.
Received: 3 July 1998 / Accepted: 30 November 1998 相似文献
19.
Kenth Dimberg Lars B. Höglund 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1987,157(4):405-412
Summary Carbonic anhydrase (CA) activities in gills and venous blood, acid-base balance, and haematological variables were studied during environmental hypercapnia in rainbow trout (Salmo gairdneri). Batches of 8–10 fish were exposed to about 3 or 13 mmHg
in flow-through tests of various duration from 4 h to 80 days.After initial acidosis, blood pH rose above pre-experimental values. At 3 mmHg it became normal again within 21 days, while at 13 mmHg the overshoot lasted for 80 days. In fish acclimated for 3 weeks or more to 13 mmHg
, blood HCO
3
–
increased four to five times while plasma Cl– levels were lower and K+ higher. Na+ levels did not show any consistent trend associated with exposure to hypercapnia. After an initial acidaemia, Hct, Hb, and RBC remained relatively constant.Patterns of change in CA activity differed between gills and erythrocytes. Initially, blood CA decreased at both
levels. It then began rising after about 3 weeks and tended to reach pre-experimental values by 80 day's hypercapnia. At 13 mmHg
, gill CA increased to twice the pre-experimental level. Compared with blood CA, gill CA appeared to be more specifically involved in fish acclimation to hypercapnia, which demands an increase in blood bicarbonate to provide a sufficient buffering capacity. Increased CA indicates that the gill enzyme may play a more important role than blood CA in acid-base regulation in fish during hypercapnia.Abbreviations
CA
carbonic anhydrase
-
Hb
haemoglobin
-
Hct
haematocrit value
-
RBC
red blood cells 相似文献
20.
The role of gill chloride cells (CCs) and pavement cells (PVCs) in acid-base regulation was evaluated in brown bullhead catfish (Ictalurus nebulosus) subjected to acute hypercapnia (water Pco2=15 torr). Chronic (10 day) cortisol treatment was used as a tool to cause CC proliferation to permit a comparison of the regulatory capacities in groups of fish with widely different gill CC populations. Cortisol (4mg kg?1 day?1) caused a pronounced increase (170%) in the surface area of CCs exposed to the water based on scanning and transmission electron microscope analysis. The density of PVC apical membrane microvilli was significantly increased (20%) by cortisol treatment. Exposure of either group of fish to hypercapnia caused similar changes in gill epithelial morphology including: (i) a marked reduction in the surface area of exposed CCs (52 and 78% reduction in the control and cortisol-treated fish, respectively); and (ii) pronounced increases in PVC apical membrane microvilli density (21 and 27% in the control and cortisol-treated fish, respectively). The rates of Cl? uptake (Jincl?) and Na+ uptake (JinNa+) were elevated (150 and 262%, respectively) in the cortisol-treated fish. Regardless of treatment, Jincl? was markedly reduced to approximately the same levels after 6 h of hypercapnia, JinNa+ was stimulated in the control group and reduced in the cortisol-treated group and thus, after 6 h of hypercapnia, JinNa+ was equal in each group. The similar morphological responses in fish possessing different initial populations suggests that the predominant mechanism of acid-base regulation during hypercapnia, reduction of C1?/HCO3? exchange, is accomplished by removal of the CC-associated C1-/HCO3? exchange sites from the water. The increase in PVC microvilli density during hypercapnia suggests a role for the PVC in acid-base regulation. 相似文献