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1.
Summary The ability of early proximal tubule cells of theNecturus kidney to regulate volume was evaluated using light microscopy, video analysis and conventional microelectrodes.Necturus proximal tubule cells regulate volume in both hyperand hyposmotic solutions. Volume regulation in hyperosmotic fluids is HCO
3
–
dependent and is associated with a decrease in the relative K+ conductance of the basolateral cell membrane and a decrease in the resistance ratio,R
a
/R
bl
. Volume regulation in hyposmotic solutions is also dependent upon the presence of HCO
3
–
but is also inhibited by 2mm Ba2+ in the basolateral solution. Hyposmotic regulation is accompanied by an increase in the relative K+ conductance of the basolateral cell membrane and an increase inR
a
/R
bl
. Neither hypo- nor hyposmotic regulation have any affect on the depolarization of the basolateral cell membrane potential induced by HCO
3
–
removal. We conclude that volume regulation in the early proximal tubule of the kidney involves both HCO
3
–
-dependent transport systems and the basolateral K+ conductance. 相似文献
2.
Previous studies in chick embryo cardiac myocytes have shown that the inhibition of Na+/K+-ATPase with ouabain induces cell shrinkage in an isosmotic environment (290 mOsm). The same inhibition produces an enhanced RVD (regulatory volume decrease) in hyposmotic conditions (100 mOsm). It is also known that submitting chick embryo cardiomyocytes to a hyperosmotic solution induces shrinkage and a concurrent intracellular alkalization. The objective of this study was to evaluate the involvement of intracellular pH (pHi), intracellular Ca2+ ([Ca2+]i) and Na+/K+-ATPase inhibition during hyposmotic swelling. Changes in intracellular pH and Ca2+ were monitored using BCECF and fura-2, respectively. The addition of ouabain (100 M) under both isosmotic and hyposmotic stimuli resulted in a large increase in [Ca2+]i (200%). A decrease in pHi (from 7.3 ± 0.09 to 6.4 ± 0.08, n = 6; p < 0.05) was only observed when ouabain was applied during hyposmotic swelling. This acidification was prevented by the removal of extracellular Ca2+. Inhibition of Na+/H2+ exchange with amiloride (1 mM) had no effect on the ouabain-induced acidification. Preventing the mitochondrial accumulation of Ca2+ using CCCP (10 M) resulted in a blockade of the progressive acidification normally induced by ouabain. The inhibition of mitochondrial membrane K+/H+ exchange with DCCD (1 mM) also completely prevented the acidification. Our results suggest that intracellular acidification upon cell swelling is mediated by an initial Ca2+ influx via Na+/Ca2+ exchange, which under hyposmotic conditions activates the K+ and Ca2+ mitochondrial exchange systems (K+/H+ and Ca2+/H+).Deceased 相似文献
3.
Ruben J. Torres Muthangi Subramanyam Guillermo A. Altenberg Luis Reuss 《The Journal of general physiology》1997,109(1):61-72
Necturus gallbladder epithelial cells bathed in 10 mM HCO3/1% CO2 display sizable basolateral membrane conductances for Cl− (GCl
b) and K + (GK
b). Lowering the osmolality of the apical bathing solution hyperpolarized both apical and basolateral membranes and increased the K +/Cl− selectivity of the basolateral membrane. Hyperosmotic solutions had the opposite effects. Intracellular free-calcium concentration ([Ca2+]i) increased transiently during hyposmotic swelling (peak at ∼30 s, return to baseline within ∼90 s), but chelation of cell Ca2+ did not prevent the membrane hyperpolarization elicited by the hyposmotic solution. Cable analysis experiments showed that the electrical resistance of the basolateral membrane decreased during hyposmotic swelling and increased during hyperosmotic shrinkage, whereas the apical membrane resistance was unchanged in hyposmotic solution and decreased in hyperosmotic solution. We assessed changes in cell volume in the epithelium by measuring changes in the intracellular concentration of an impermeant cation (tetramethylammonium), and in isolated polarized cells measuring changes in intracellular calcein fluorescence, and observed that these epithelial cells do not undergo measurable volume regulation over 10–12 min after osmotic swelling. Depolarization of the basolateral membrane voltage (Vcs) produced a significant increase in the change in Vcs elicited by lowering basolateral solution [Cl−], whereas hyperpolarization of Vcs had the opposite effect. These results suggest that: (a) Hyposmotic swelling increases GK
b and decreases G Cl
b. These two effects appear to be linked, i.e., the increase in G K
b produces membrane hyperpolarization, which in turn reduces G Cl
b. ( b) Hyperosmotic shrinkage has the opposite effects on GK
b and G Cl
b. ( c) Cell swelling causes a transient increase in [Ca2+]i, but this response may not be necessary for the increase in GK
b during cell swelling. 相似文献
4.
Background and aims
Steroid hormones target K+ channels as a means of regulating electrolyte and fluid transport. In this study, ion transporter targets of Estradiol (E2) were investigated in the human eccrine sweat gland cell line NCL-SG3.Results
Whole cell patch-clamp studies revealed E2 (10 nM) rapidly activates a whole cell K+ conductance, which is abolished by clotrimazole (30 μM), an inhibitor of the intermediate conductance calcium activated K+ channel (IKCa). The estrogen receptor (ER) antagonist ICI 182, 780 had no effect on this E2 activated K+ conductance, suggesting an estrogen receptor independent mechanism of activation. Confocal microscopy studies revealed under basal conditions that the IKCa channel is located within the cell cytoplasm and in the presence of E2, rapidly translocates to both the apical and basolateral membrane. In the presence of E2, tyrosine phosphorylation of calmodulin, which is known to regulate trafficking of the IKCa channel, is increased, and treatment of cells with the calmodulin inhibitor trifluoperazine (TFP) prevents the E2-induced translocation.Conclusions
Estradiol rapidly regulates a K+ conductance through the IKCa channel in an estrogen receptor independent manner. E2 stimulates the translocation of IKCa to the cell membrane in a calmodulin dependent manner, representing a novel paradigm of estrogen action in sweat gland epithelial cells. 相似文献5.
Adrian Caplanusi Kwang-Jin Kim Els Lariviere Willy Van Driessche Danny Jans 《The Journal of membrane biology》2006,214(1-2):33-41
This study describes the correlation between cell swelling-induced K+ efflux and volume regulation efficiency evaluated with agents known to modulate ion channel activity and/or intracellular
signaling processes in a human bronchial epithelial cell line, 16HBE14o−1. Cells on permeable filter supports, differentiated into polarized monolayers, were monitored continuously at room temperature
for changes in cell height (Tc), as an index of cell volume, whereas 86Rb efflux was assessed for K+ channel activity. The sudden reduction in osmolality of both the apical and basolateral perfusates (from 290 to 170 mosmol/kg
H2O) evoked a rapid increase in cell volume by 35%. Subsequently, the regulatory volume decrease (RVD) restored cell volume
almost completely (to 94% of the isosmotic value). The basolateral 86Rb efflux markedly increased during the hyposmotic shock, from 0.50 ± 0.03 min−1 to a peak value of 6.32 ± 0.07 min−1, while apical 86Rb efflux was negligible. Channel blockers, such as GdCl3 (0.5 mM), quinine (0.5 mM) and 5-nitro-2-(3-phenyl-propylamino) benzoic acid (NPPB, 100 μM), abolished the RVD. The protein tyrosine kinase inhibitors tyrphostin 23 (100 μM) and genistein (150 μM) attenuated the RVD. All agents decreased variably the hyposmosis-induced elevation in 86Rb efflux, whereas NPPB induced a complete block, suggesting a link between basolateral K+ and Cl−1 efflux. Forskolin-mediated activation of adenylyl cyclase stimulated the RVD with a concomitant increase in basolateral 86Rb efflux. These data suggest that the basolateral extrusion of K+ and Cl−1 from 16HBE14o−1 cells in response to cell swelling determines RVD efficiency. 相似文献
6.
Bacová Z Kiss A Jamal B Payer J Strbák V 《Cellular and molecular neurobiology》2006,26(4-6):1045-1053
Summary 1. Cell swelling induces exocytosis of material stored in secretory vesicles resulting in a secretory burst of peptidic hormones or enzymes from various types of cells including endocrine cells and neurons. We have previously shown that swelling-induced exocytosis possesses limited selectivity; hypotonic medium evokes TRH but not oxytocin release from hypothalamic paraventricular nucleus (PVN) and neurohypophysis (NH).2. It is the aim of this study to ascertain whether the swelling-induced oxytocin secretion could be unmasked by the inhibition of specific osmotic response using Ca2+-free medium and GdCl3, an inhibitor of stretch activated channels.3. Oxytocin release from the PVN was stimulated by the hypotonic medium only in the presence of 50 or 100 μM GdCl3. Oxytocin release from supraoptic nucleus (SON) was also stimulated by the Ca2+-free hypotonic medium in the presence of GdCl3. Oxytocin secretion from the NH was not stimulated even in the presence of GdCl3, both in Ca2+ containing and Ca2+-free medium. TRH response to swelling-inducing stimulus was not affected by the presence of GdCl3.4. An intranuclear oxytocin secretion to hyposmotic stimulation within the PVN and the SON could be unmasked by the inhibiting specific response by GdCl3. At these conditions general secretory response to swelling-inducing stimuli emerged. Secretion of oxytocin from the NH was not affected by any of these treatments.5. Peptides and proteins released after cell swelling can play an important role in the pathophysiology of ischemia and could be mediators of local or remote preconditioning. Disruption of mechanosensitive gating in magnocellular neurosecretory cells could result in an inadequate secretory response (e.g. stimulation instead of inhibition and vice versa) of hormones engaged in water and salt metabolism regulation. 相似文献
7.
The effect of hyposmotic and isosmotic cell swelling on the free intracellular calcium concentration ([Ca2+]i) in rat mammary acinar cells has been examined using the fura-2 dye technique. A hyposmotic shock (40% reduction) increased the [Ca2+]i in rat mammary acinar cells in a fashion which was transient; the [Ca2+]i returned to a value similar to that found under isomotic conditions within 180 sec. The increase in the [Ca2+]i was dependent upon the extent of the osmotic shock. The hyposmotically-activated increase in the [Ca2+]i could not be attributed to a reduction in extracellular Na+ or a change in the ionic strength of the incubation medium. Thapsigargin (1 M) enhanced the hyposmotically-activated increase in the [Ca2+]i. Isosmotic swelling of rat mammary acinar cells, using urea, had no significant effect on the [Ca2+]i. Similarly, a hyperosmotic shock did not affect the [Ca2+]i in rat mammary acinar cells. It appears that the effect of cell swelling on the [Ca2+]i in rat mammary acinar cells depends on how the cells are swollen (hyposmotic vs. isosmotic). This finding may have important physiological implications given that it is predicted that mammary cell volume will change in vivo under isomotic conditions. 相似文献
8.
Roberto Sánchez-Olea Herminia Pasantes-Morales Prof. Arne Schousboe 《Neurochemical research》1993,18(2):147-152
The effect of hyposmotic conditions on the concentration of intracellular free calcium ([Ca2+]i) was studied in cultured cerebellar granule cells and cerebral cortical neurons after loading of the cells with the fluorescent Ca2+ chelator Fluo-3. It was found that in both types of neurons exposure to media with a decrease in osmolarity of 20 to 50% of the osmolarity in the isosmotic medium (320 mOsm) led to a dose dependent increase in [Ca2+]i with a time course showing the highest value at the earliest measured time point, i.e. 40 s after exposure to the hyposmotic media and a subsequent decline towards the basal level during the following 320 s. The response in the cortical neurons was larger than in the granule cells but both types of neurons exhibited a similar increase in [Ca2+]i after expoxure to 50 mM K+ which was of the same magnitude as the increase in [Ca2+]i observed in the cortical neurons exposed for 40 s to a medium with a 50% reduction in osmolarity. In both types of neurons the blocker of voltage gated Ca2+ channels verapamil had no effect on the hyposmolarity induced increase in [Ca2+]i. On the contrary, this increase in [Ca2+]i was dependent upon external calcium and could be inhibited partly or completely by the inorganic blockers of Ca2+ channels Mg2+ and La3+. Dantrolene which prevents release of Ca2+ from internal stores had no effect. The results show that exposure of neurons to hyposmotic conditions leading to swelling results in a large increase in free intracellular Ca2+ which represents an influx of Ca2+ rather than a release of Ca2+ from internal, dantrolene sensitive stores. 相似文献
9.
Roy K. Cheung Sergio Grinstein Hans-Michael Dosch Erwin W. Gelfand 《Journal of cellular physiology》1982,112(2):189-196
The mechanism of volume regulation in hypotonic media was analysed in human peripheral blood mononuclear (PBM) cells. Electronic cell sizing showed that hypotonic swelling is followed by a regulatory volume decrease (RVD) phase. This was confirmed by both electron microscopy and by cellular water determinations. The rate of regulatory shrinking was proportional to the degree of hypotonicity in the 0.5–0.9 X isotonic range. Cell viability was only marginally affected in this range. The content of cellular K+ decreased during RVD, while Na+ content remained unchanged. Similarly, the efflux of 86Rb (used as a K+ analog) increased upon dilution, whereas 22Na efflux was not altered. 86Rb uptake was enhanced by hypotonic stress and both ouabain-sensitive and -insensitive components were affected. A ouabain-sensitive stimulation was also seen in Na+- free media. Ouabain partially inhibited RVD only if added to the cells hours before hypotonic challenge. A normal shrinking response was observed in K+-free media, and also in Na+-free media when Li+, choline+, or Tris+ were the substitutes. In high K+ or Rb+ hypotonic media shrinking was absent and a second swelling phase was observed. Cs+ displayed an intermediate behavior, with shrinking observed at lower dilutions and secondary swelling at higher ones. The direction and magnitude of the response also changed when the external K+ concentration was varied and, with 50 mM K+, no regulatory volume change occurred following hypotonic stress. These findings suggest that RVD occurs largely by a passive loss of cellular K+, resulting from a selective increase in permeability to this ion. In addition, the (Na-K) pump appears to be activated upon cell swelling by a mechanism other than Na+ entry into the cell, but this activation is not essential for RVD. 相似文献
10.
The Na+ and K+ permeability properties of rat brain mitochondria were determined to explain the influences of these cations upon respiration. A new procedure for isolating exceptionally intact mitochondria with minimal contamination by synaptosomes was developed for this purpose.Respiration was uncoupled by Na+ and less so by K+. Uncoupling was maximal in the presence of EDTA plus Pi and was decreased by Mg2+. Maximal uncoupler-stimulated respiration rates were inhibited by Na+ but largely unaffected by K+. The inhibition by Na+ was relatively insensitive to Mg2+. Membrane Na+ and K+ conductances as well as neutral exchanges (Na+/H+ and K+/H+ antiport activities) were determined by swelling measurements and correlated with metabolic effects of the cations.Cation conductance, i.e. electrophoretic Na+ or K+ permeation, was increased by EDTA (Na+ > K+) and decreased by Mg2+. Magnesium preferentially suppressed Na+ conductance so as to reverse the cation selectivity (K+ > Na+). Neutral cation/H+ exchange rates (Na+ > K+) were not influenced by chelator or Mg2+.The extent of cation-dependent uncoupling of respiration correlated best with the inner membrane conductance of the ion according to an empirical relationship derived with the model K+ conductor valinomycin. The metabolic influences of Na+ and K+ can be explained in terms of coupled flow of these ions with protons and their effect upon the H+ electrochemical gradient although alternative possibilities are discussed. These in vitro studies are compared to previous observations in situ to assess their physiological significance. 相似文献
11.
Membrane transport changes in human lens epithelial (HLE‐B3) cells under hyposmotic and apoptotic stress were compared. Cell potassium content, Ki, uptake of the K congener rubidium, Rbi, and water content were measured after hyposmotic stress induced by hypotonicity, and apoptotic stress by the protein‐kinase inhibitor staurosporine (STP). Cell water increased in hyposmotic (150 mOsm) as compared to isosmotic (300 mOsm) balanced salt solution (BSS) by >2‐fold at 5 min and decreased within 15 min to baseline values accompanied by a 40% Ki loss commensurate with cell swelling and subsequent cell shrinkage likely due to regulatory volume decrease (RVD). Loss of Ki, and accompanying water, and Rbi uptake in hyposmotic BSS were prevented by clotrimazole (CTZ) suggesting water shifts associated with K and Rb flux via intermediate conductance K (IK) channels, also detected at the mRNA and protein level. In contrast, 2 h after 2 µM STP exposure, the cells lost ~40% water and ~60% Ki, respectively, consistent with apoptotic volume decrease (AVD). Indeed, water and Ki loss was at least fivefold greater after hyposmotic than after apoptotic stress. High extracellular K and 2 mM 4‐aminopyridine (4‐AP) but not CTZ significantly reduced apoptosis. Annexin labeling phosphatidylserine (PS) at 15 min suggested loss of lipid asymmetry. Quantitative PCR revealed significant IK channel expression during prolonged hyposmotic stress. Results suggest in HLE‐B3 cells, IK channels likely partook in and were down regulated after RVD, whereas pro‐apoptotic STP‐activation of 4‐AP‐sensitive voltage‐gated K channels preceded or accompanied PS externalization before subsequent apoptosis. J. Cell. Physiol. 223: 110–122, 2010. © 2009 Wiley‐Liss, Inc. 相似文献
12.
Electron probe X-ray microanalysis was used to analyse the effects of sub-zero temperatures on K+ distribution in compartments within non-acclimated and cold acclimated rye (Secale cereale L. cv Voima) leaf cells and to evaluate membrane leakage of ions caused by freezing-injury. The specimens were rapidly frozen from growing temperatures and from two different sub-zero temperatures (LT50 and LT100) to which the leaves had already been slowly cooled. Measurements were made in the cytoplasm, vacuole and cell walls in freeze-substituted mesophyll cells. At ambient temperatures, the mean K+ concentration in the cytoplasm (100 mol m?3) differed significantly from that of the vacuole (49 mol m?3) in the non-acclimated (NA) cells, while in cold acclimated (A) cells, the concentrations were similar (109 vs 93 mol m?3, respectively). At LT50 temperatures, the K+ concentration in NA-cells decreased significantly in the cytoplasm (59 mol m?3) but increased in the cell walls. In the A-cells, on the other hand, the mean K+ concentration increased significantly (about three-fold) in all major compartments. At LT100 temperatures, K+ concentrations in the cytoplasm and cell walls decreased when compared with corresponding LT50 values in the A-cells but increased in the NA-cells. The increased potassium concentration in the cytoplasm of A-cells at LT50 temperature is compatible with the observed cell shrinkage and an absence of plasma membrane damage. The decreased potassium concentration in the cytoplasm of NA-cells at LT50 temperature is compatible with the slight cell shrinkage and suggests that the plasma membrane in these cells shows increased permeability due to freeze injury. 相似文献
13.
Cells of the salt-tolerant charophyte Lamprothamnium respond differently to hypotonic challenge according to their position on the plant (i.e. cell age). Differences in electrophysiological response are coupled with differences in cell fine structure, and the presence or absence of extracellular mucilage. (1) Young, apical (fast-regulating, FR) cells respond with sudden cessation of cyclosis, depolarization to –50 mV (in some cells by more than 100 mV) and increase in membrane conductance by up to an order of magnitude. Intracellular [K+]v, [Na+]v and [Cl–]v decrease 1 h after hypotonic challenge. Patch-clamping cytoplasmic droplets reveals two types of K+ channel, 150 pS and 35 pS, and a small conductance Cl– channel, 35 pS (conductances at estimated tonoplast resting potential between zero and 20 mV). Extracellular mucilage is thin (< 5 μm thick) or lacking, similar to freshwater Chara. Unlike freshwater charophytes these cells have a canalicular vacuolar system of large surface area and compartment the fluorochrome 6 carboxyfluorescein in the cytoplasm rather than the vacuolar system. (2) Older basal (slow-regulating, SR) cells do not cease streaming on hypotonic challenge and depolarize only slightly (by approximately 20 mV) with small or no change in membrane conductance. After 1 h the intracellular [K+]v, [Na+]v and [Cl–]v scarcely change. Patch-clamping cytoplasmic droplets reveals two types of K+ channel, medium conductance 90 pS and low conductance (as in FR cells). The large conductance K+ channel was not observed. The Cl– channel was more active in SR cells. The cells were coated with extracellular mucilage more than 10 μm thick. In a similar manner to freshwater Chara, these cells compartment 6 carboxyfluorescein in a large central vacuole. In the older cells, making up the bulk of any given plant, the simultaneous development of extracellular mucilage and a large central vacuole which compartments 6 carboxyfluorescein is associated with a minimal electrophysiological response to hypotonic challenge. The significance of these findings for salt-tolerance is discussed. 相似文献
14.
I.F. Gow 《生物化学与生物物理学报:生物膜》2005,1712(1):52-61
The effect of a hyposmotic shock and extracellular ATP on the efflux of K+(Rb+) from human breast cancer cell lines (MDA-MB-231 and MCF-7) has been examined. A hyposmotic shock increased the fractional efflux of K+(Rb+) from MDA-MB-231 cells via a pathway which was unaffected by Cl− replacement. Apamin, charybdotoxin or removing extracellular Ca2+ had no effect on volume-activated K+(Rb+) efflux MDA-MB-231 cells. An osmotic shock also stimulated K+(Rb+) efflux from MCF-7 cells but to a much lesser extent than found with MDA-MB-231 cells. ATP-stimulated K+(Rb+) efflux from MDA-MB-231 cells in a dose-dependent fashion but had little effect on K+(Rb+) release from MCF-7 cells. ATP-stimulated K+(Rb+) efflux was only inhibited slightly by replacing Cl− with NO3−. Removal of external Ca2+ during treatment with ATP reduced the fractional efflux of K+(Rb+) in a manner suggesting a role for cellular Ca2+ stores. Charybdotoxin, but neither apamin nor iberiotoxin, inhibited ATP-stimulated K+(Rb+) release from MDA-MB-231 cells. Suramin inhibited the ATP-activated efflux of K+(Rb+). UTP also stimulated K+(Rb+) efflux from MDA-MB-231 cells whereas ADP, AMP and adenosine were without effect. A combination of an osmotic shock and ATP increased the fractional efflux of K+(Rb+) to a level greater than the sum of the individual treatments. It appears that the hyposmotically-activated and ATP-stimulated K+ efflux pathways are separate entities. However, there may be a degree of ‘crosstalk’ between the two pathways. 相似文献
15.
Barley roots contain a CO2 sensitive respiratory fraction which is inhibited in 50 per cent CO2 and is partially restored upon subsequent exposure to air. The residual O2 consumption occurring at CO2 concentrations between 50 per cent and 95 per cent amounts to about 40 per cent of the O2 uptake in air and can support K+ uptake for a limited time at a rate equal to or higher than occurs in air. Above 95 per cent CO2 both O2 and K+ uptakes decrease rapidly. 2,4-dinitrophenol (DNP), in the range of 10?6 to 10?5M, stimulates O2 uptake by the roots in air. The stimulation is absent when roots are treated with DNP in 80 per cent CO2, presumably because of the reduced demand for inorganic phosphate and phosphate acceptor at the lower respiratory level in high CO2. In either air or CO2, K+ uptake is strongly inhibited by DNP. A comparison of the respiratory and K+ uptake data indicates that O2 consumption is a necessary requirement for the uptake process in high CO2. Protoplasmic streaming in the root cells is rapidly stopped by high CO2 although K+ uptake and O2 consumption continue. The cation uptake mechanism in high CO2 appears to be limited to the stationary cytoplasm. It is also possible that a similar mechanism may be involved in cation uptake in air. 相似文献
16.
Summary The outward rectification of the K+ current in mesophyll cell protoplasts from trap-lobes ofDionaea muscipula was studied with the patch-clamp technique. The rectification had instantaneous and time-dependent components. Changes in [K+]
i
strongly affected the conductance voltage relation of the plasma membrane while changes in [K+]
o
had little effect on the relation. Thus, the outward rectification depends on the membrane voltage and the concentration of intracellular K+. Corresponding single-channel activities were observed both in the intact membrane (cell-attached recording) and in excised patches. The single-channel conductance was about 3.3 pS with symmetrical solutions containing 30mm K+. 相似文献
17.
T.E. DeCoursey S.Y. Kim M.R. Silver F.N. Quandt 《The Journal of membrane biology》1996,152(2):141-157
Ion channel expression was studied in THP-1 human monocytic leukemia cells induced to differentiate into macrophage-like cells
by exposure to the phorbol ester, phorbol 12-myristate 13-acetate (PMA). Inactivating delayed rectifier K+ currents, I
DR, present in almost all undifferentiated THP-1 monocytes, were absent from PMA-differentiated macrophages. Two K+ channels were observed in THP-1 cells only after differentiation into macrophages, an inwardly rectifying K+ channel (I
IR) and a Ca2+-activated maxi-K channel (I
BK). I
IR was a classical inward rectifier, conducting large inward currents negative to E
K and very small outward currents. I
IR was blocked in a voltage-dependent manner by Cs+, Na+, and Ba2+, block increasing with hyperpolarization. Block by Na+ and Ba2+ was time-dependent, whereas Cs+ block was too fast to resolve. Rb+ was sparingly permeant. In cell-attached patches with high [K+] in the pipette, the single I
IR channel conductance was ∼30 pS and no outward current could be detected. I
BK channels were observed in cell-attached or inside-out patches and in whole-cell configuration. In cell-attached patches the
conductance was ∼200–250 pS and at potentials positive to ∼100 mV a negative slope conductance of the unitary current was
observed, suggesting block by intracellular Na+. I
BK was activated at large positive potentials in cell-attached patches; in inside-out patches the voltage-activation relationship
was shifted to more negative potentials by increased [Ca2+]. Macroscopic I
BK was blocked by external TEA+ with half block at 0.35 mm. THP-1 cells were found to contain mRNA for Kv1.3 and IRK1. Levels of mRNA coding for these K+ channels were studied by competitive PCR (polymerase chain reaction), and were found to change upon differentiation in the
same direction as did channel expression: IRK1 mRNA increased at least 5-fold, and Kv1.3 mRNA decreased on average 7-fold.
Possible functional correlates of the changes in ion channel expression during differentiation of THP-1 cells are discussed.
Received: 19 September 1995/Revised: 14 March 1996 相似文献
18.
Leaflet movements in Samanea saman are driven by the shrinking and swelling of cells in opposing (extensor and flexor) regions of the motor organ (pulvinus). Changes in cell volume, in turn, depend upon large changes in motor cell content of K+, Cl− and other ions. We performed patch-clamp experiments on extensor and flexor protoplasts, to determine whether their plasma membranes contain channels capable of carrying the large K+ currents that flow during leaflet movement. Recordings in the “whole-cell” mode reveal depolarization-activated K+ currents in extensor and flexor cells that increase slowly (t½ = ca. 2 seconds) and remain active for minutes. Recordings from excised patches reveal a single channel conductance of ca. 20 picosiemens in both cell types. The magnitude of the K+ currents is adequate to account quantitatively for K+ loss, previously measured in vivo during cell shrinkage. The K+ channel blockers tetraethylammonium (5 millimolar) or quinine (1 millimolar) blocked channel opening and decreased light- and dark-promoted movements of excised leaflets. These results provide evidence for the role of potassium channels in leaflet movement. 相似文献
19.
Wolfram Nagel 《生物化学与生物物理学报:生物膜》1979,552(2):346-357
The effect of Ba2+ (0.5 mM, corial side) upon the transport characteristics of the frog skin epithelium was investigated. It was observed that Ba2+ decreased the conductance of the preferably K+-permeable basolateral border to less than 30% of its control value. Furthermore, Ba2+ abolished the K+ electrode-like behaviour, existing at the basolateral membrane under conditions of zero transcellular current flow, for [K+] below 10–15 mM. Effects upon other parameters of transepithelial transport (electromotive forces and resistance of outer or basolateral border and shunt pathway, respectively) were small and might represent secondary events. It is concluded that Ba2+ inhibits passive fluxes of K+ across basolateral membranes of tight, Na+ transporting epithelia, similar to its influence upon membranes of nonpolar cells. 相似文献
20.
Mechanosensitive channels, inner membrane proteins of bacteria, open and close in response to mechanical stimuli such as changes in membrane tension during osmotic stress. In bacteria, these channels act as safety valves preventing cell lysis upon hypoosmotic cell swelling: the channels open under membrane tension to release osmolytes along with water. The mechanosensitive channel of small conductance, MscS, consists, in addition to the transmembrane channel, of a large cytoplasmic domain (CD) that features a balloon-like, water filled chamber opening to the cytoplasm through seven side pores and a small distal pore. The CD is apparently a molecular sieve covering the channel that optimizes loss of osmolytes during osmoadaptation. We employ diffusion theory and molecular dynamics simulations to explore the transport kinetics of Glu− and K+ as representative osmolytes. We suggest that the CD indeed acts as a filter that actually balances passage of Glu− and K+, and possibly other positive and negative osmolytes, to yield a largely neutral efflux and, thereby, reduce cell depolarization in the open state and conserve to a large degree the essential metabolite Glu−. 相似文献