Influence of deionized water supplemented or not with different ions on prolactin cell activity and osmotic regulation in the goldfish

• 1.1. Goldfish were kept in deionized water (DW), DW + Na⁺ (0.35 mM), DW + K⁺ (0.05 mM), DW + Ca²⁺ (2mM) and DW + Mg²⁺ (0.2 mM). In Ca-free environments, prolactin cells appear unaffected. Stimulated calcium-sensitive cells (pars intermedia) may elaborate a hypercalcemic factor.
• 2.2. Fecal excretion, reduced in all groups, remains noticeable in DW + Ca²⁺
• 3.3. Ionic losses, very low in all groups, are minimal in DW. Supplementation with K⁺ increases Na⁺ loss.
• 4.4. Plasma Na⁺ Ca²⁺, and osmolarity decrease in DW, and still more in DW + K⁺. Ca²⁺' and Mg²⁺ partly suppress hyponatremia.
• 5.5. In goldfish kept in DW and subsequently in DW + Ca²⁺, calcemia increases.

     

Synaptic transmission at high pressure: Effects of [Ca2+]o

• 1.1. The effects of pressure on synaptic currents were examined in crayfish abdominal muscles.
• 2.2. Helium pressure (10.1 MPa) considerably decreased extracellulariy-recorded excitatory junctional potentials associated with increased short-term facilitation.
• 3.3. These effects could be mimicked by a reduction of [Ca²⁺]_o, and partially compensated by an increase in [Ca²⁺]_o.
• 4.4. Pressure also reduced the amplitude of the extracellular nerve terminal potentials (ENTP) by up to 25%, and significantly increased synaptic delay in a [Ca²⁺]_o-dependent manner.
• 5.5. The interaction between compression and various [Ca²⁺]_o were analysed in terms of an existing model of transmitter release. The results were consistent with the hypothesis that high pressure decreases the maximal Ca²⁺ influx into nerve terminals.
• 6.6. The decreased ENTP and increased synaptic delay suggest that additional processes may be involved in pressure effects on synaptic transmission.

     

Inhibitors of active Ca2+ uptake by fragments of the sarcoplasmic reticulum of lobster muscle

• 1.1. Vesicles from the sarcoplasmic reticulum of lobster muscle accumulate Ca²⁺ if supplied with ATP as an energy source. A search was undertaken for inhibitors of Ca²⁺ transport.
• 2.2. p-Hydroxymercuribenzoate can completely inhibit Ca²⁺ transport and ATP hydrolysis. 2–4 Dinitrophenol inhibits uptake but not hydrolysis.
• 3.3. Sr²⁺, Ba²⁺ and Zn²⁺ inhibit uptake, perhaps by competing with Ca²⁺ for a carrier.
• 4.4. The vesicles contain acetylcholinesterase. Anticholinesterases can reduce —but not abolish—Ca²⁺ uptake. Acetylcholine has no effect on the activity of the vesicles.
• 5.5. Ca²⁺ uptake is not affected by Mn²⁺, glutamate, pilocarpine, carnosine, caffeine, strophanthidin or tetraethylammonium.
• 6.6. K⁺ is needed for maximal activity of the uptake system but not for ATP hydrolysis. Apparently K⁺ enhances the coupling between the energy supply and the carrier mechanism.

     

Potassium channels in growth cones of leech retzius cells

• 1.1. Potassium-selective channels were analysed in growth cones of cultured leech Retzius cells.
• 2.2. In the cell-attached mode and at physiological bath and pipette solution little channel activity was observed at resting membrane potential. The channel open probability (p_o) increased with cell depolarization, and the slope conductance of the single K⁺ channel current was about 60 pS.
• 3.3. With symmetrical high KCl solution on both sides of the excised membrane patch three K⁺ -selective channels could be discriminated. Two channels exhibited a linear current-voltage relation of about 18 pS and 106 pS, respectively.
• 4.4. The most frequently observed K⁺ channel showed a non-linear current-voltage relation and p_o increased with increasing free cytoplasmic Ca²⁺ and during cell hyperpolarization.

     

The exchange of radioactive cations by somatic and cardiac muscles of the crayfish

• 1.1. Intracellular concentrations of Na⁺, K⁺, Ca²⁺ and Mg²⁺ were measured in a somatic muscle and in the heart of the crayfish. The uptake and the efflux of Na²⁴, K⁴², Ca⁴⁵ and of Sr⁸⁹ were also measured.
• 2.2. The initial influx rates of the ions from van Harreveld's solution into resting somatic muscle (in μEq/g cell water/hr) are: K⁺ = 25; Na⁺ = 56; Ca²⁺ = 38. Similar figures were obtained for the heart muscle.
• 3.3. The calculated permeability constants (× 10⁸ cm/sec) are: P_K = 64; P_Na = 30 P_Ca = 10; P_Sr = 1·5.
• 4.4. The stimulation of the muscle fiber leads to an additional Ca²⁺ influx of about 2·8 pEq/cm² fiber surface. The additional Ca²⁺ uptake is sufficient to account for the change in potential on the membrane.
• 5.5. When muscles were immersed in Sr²⁺ solutions, no additional Sr⁸⁹ uptake was found with stimulation. However, there is a high resting Sr⁸⁹ uptake and the muscle in Sr²⁺ has a long refractory period, so a reasonable increase in Sr⁸⁹ uptake would not be detectable.
• 6.6. The results are discussed in relation to the divalent cation mechanism for generating action potentials and to the part played by Ca²⁺ in triggering contraction.

     

Effects of K+, Ba2+ and Ca2+ on the excitable membrane in Paramecium tetraurelia

• 1.1. The effects of Ba²⁺ and K⁺ ions on the membrane currents of Paramecium tetraurelia under a voltage clamp were investigated.
• 2.2. External Ba²⁺ suppresses the inward-going K-current and the Ca-induced K-outward current and changes the activation and inactivation kinetics of transient inward current through the Ca-channel.
• 3.3. K⁺ increases the Ca-induced K-conductances but little affects the leakage conductance.
• 4.4. The resting potentials by changing those ionic concentrations shift the voltage sensitivities of all voltage sensitive channels, simultaneously.
• 5.5. The competition between ions to the channel responses was discussed.

     

Osmoregulation in the brook trout,Salvelinus fontinalis—II. Effects of size,age and photoperiod on seawater survival and ionic regulation

• 1.1. Brook trout (Salvelinus fontinalis) of a single genetic stock, and hatched at the same time, were raised under two photoperiod and two feeding regimes to obtain fish of the same age but with different sizes and photoperiod experiences. In 11 experiments over 1.5 firs, fish were gradually exposed to 32 ppt seawater for 20 days to investigate the ontogeny of salinity tolerance.
• 2.2. Daily changes in plasma osmolarity, [Na⁺], [Cl⁻], [K⁺], [Mg²⁺], thyroxine, hematocrit and gill Na⁺,K⁺-ATPase during adaptation to 10, 20 and 32 ppt were examined in one experiment.
• 3.3. Size was the primary determinant of seawater survival (r² = 0.77) the effect of size on seawater survival slowed after fish reached a fork length of 14 cm. The effect of age on seawater survival (r² = 0.65) was through its covariance with size.
• 4.4. Photoperiod affected seawater survival only through its influence on the timing of male maturation, which decreased salinity tolerance.
• 5.5. Regulation of plasma osmolarity, [Na⁺], [Cl⁻], [K²⁺], [Mg²⁺] and hematocrit in sea water increased linearly with size over the entire range of sizes (6–32 em).
• 6.6. Gill Na⁺,K⁺-ATPase activity after 20 days in seawater decreased with increasing size of brook trout, possibly reflecting decreased demand for active ion transport in larger fish.
• 7.7. Plasma thyroxine concentrations declined in seawater, but no definitive role of this hormone in seawater adaptation was found.
• 8.8. Size dependent survival and osmoregulatory ability of brook trout is compared to other salmonids and a conceptual model is developed.

     

Modulation of the ATP induced [Ca2+]c increase in as-30D hepatoma cells

• 1.1. The regulation of the increase in the cytosolic calcium concentration ([Ca²⁺]c) induced by extracellular ATP in AS-30D hepatoma cells was studied.
• 2.2. Homologous desensitization involving the refilling of intracellular calcium pools and the participation of protein kinase C was found.
• 3.3. Isoproterenol, forskolin and dibutyril-cyclic AMP also induced an increase in [Ca²⁺]c.
• 4.4. Interestingly, synergism was found for isoproterenol or forskolin and ATP.
• 5.5. The results suggest that there are two pathways for mobilizing [Ca²⁺] in AS-30D hepatoma cells; one is activated by ATP receptors and the other by cyclic AMP.

     

Erythrocyte membrane anion-sensitive Mg2+-ATPase—Identity with monovalent cation sensitive Ca2+-Mg2+-ATPase

• 1.1. Activation of Mg²⁺-ATPase of rabbit and guinea-pig erythrocyte membrane by bicarbonate or chloride could be completely abolished by ethylene-glycol-bis-(β-aminoethylether)-N,N'-tetraacetic acid. The anion stimulation was actually an activation of contaminating Ca²⁺ -stimulated Mg²⁺-ATPase by monovalent cations associated with the anions.
• 2.2. Guinea-pig red cell Ca²⁺-Mg²⁺-ATPase could be activated by both sodium and potassium while the rabbit enzyme was sensitive only to sodium. The concentrations of monovalent cations for half-maximal stimulation of Ca²⁺-Mg²⁺-ATPase are: k_na+ = 40.8 mM, k_k+ = 12.2 mM (guinea-pig); K_Na+ = 13.3mM (rabbit).
• 3.3. Potassium enhanced activation of rabbit erythrocyte membrane Ca²⁺-Mg²⁺-ATPase by red cell Ca²⁺-Mg²⁺-ATPase activator protein. With the guinea pig enzyme, neither sodium nor potassium enhanced activator stimulation of Ca²⁺-Mg²⁺-ATPase.
• 4.4. Ca²⁺-Mg²⁺-ATPase of aged rabbit erythrocyte membrane responded to sodium but not to activator protein.
• 5.5. Triton X-100 solubilized rabbit erythrocyte membrane Ca²⁺-Mg²⁺-ATPase has an apparent molecular weight of 371,000. It did not respond to the activator.
• 6.6. One major and three minor proteins, visualized by SDS-polyacrylamide gel electrophoresis, were extracted from rabbit erythrocyte membrane by 50 μM chlorpromazine.

     

The effect on creatine kinase release of altered conditions in the Ca2+ paradox

• 1.1. Release of creatine kinase (CK) in the Ca²⁺ paradox of the Langendorff-perfused rat heart is dependent on the conditions of Ca²⁺ depletion and Ca²⁺ repletion.
• 2.2. CK release is reduced by raising [Ca²⁺]_o during Ca²⁺ depletion and progressively increased by extending the Ca²⁺ free period from 2 to 5 min.
• 3.3. CK release is reduced by decreasing the electrochemical gradient for Ca²⁺ during Ca²⁺ repletion.
• 4.4. The findings are discussed in the light of current hypotheses for the biochemical mechanisms that underlie the Ca²⁺ paradox.

     

High-affinity Ca2+-Mg2+-ATPase in kidney of euryhaline Gillichthys mirabilis: kinetics,subcellular distribution and effects of salinity

• 1.1. Two components of Ca²⁺-Mg²⁺-ATPase are observed in kidneys of G. mirabilis. The high-affinity component has a K_0.5Ca of 0.23μM; the low-affinity activity K_0.5Ca is 90–110μM. The high-affinity activity requires Mg²⁺, displays Michaelis-Menten kinetics, has peak activity at 1.2 μM Ca²⁺, and is insensitive to ouabain and Na⁺ azide.
• 2.2. In subcellular fractions, the high-affinity component segregates with Na⁺-K⁺-ATPase and is localized predominantly in BLM. The low-affinity component is broadly distributed among membranous organelles, including brush border, and may be equivalent to alkaline phosphatase.
• 3.3. Specific activity of the high-affinity Ca²⁺-Mg²⁺-ATPase is modestly increased following adaptation of fish to FW, but total renal high-affinity activity is greatest in the hypertrophied kidneys of FW-adapted fish and is least in kidneys of fish adapted to 200% SW.
• 4.4. High-affinity Ca²⁺-Mg²⁺-ATPase may be associated with active Ca²⁺ transport or with regulation of intracellular Ca²⁺ concentration of tubular cells.

     

The possibility that Ca2+-ATPase from the plasma membrane-rich fraction of bovine parotid gland is ecto-Ca2+-dependent nucleoside triphosphatase

• 1.1. Parotid plasma membrane nonpump low-affinity Ca²⁺-ATPase, which possesses high-affinity (Ca²⁺ + Mg²⁺ )-ATPase activity, was characterized.
• 2.2. Purified Ca²⁺-ATPase hydrolyzed the nucleoside triphosphates, GTP, ITP, CTP, UTP, TTP (67–93% of ATP) and nucleoside diphosphates, ADP. GDP, IDP, CDP, TDP (12–40% of ATP) but not AMP and p-NPP.
• 3.3. The maximum activities of Ca²⁺- and (Ca²⁺ +Mg²⁺ )-ATPases were obtained in the presence of 1 mM and 0.13 μ M Ca²⁺, respectively.
• 4.4. The K_m values for Ca²⁺ in Ca²⁺- and (Ca²⁺+ Mg²⁺ )-ATPases were 0.2 mM and 22 nM. respectively.
• 5.5. The activities of both Ca²⁺- and (Ca²⁺ + Mg²⁺ )-ATPases were found in the right-side-out-vesicles obtained from the plasma membrane-rich fraction.
• 6.6. These features suggest that Ca²⁺-ATPase is an ecto-Ca²⁺-dependent nucleoside triphosphatase.

     

Renal response to hypoxia in carp,Cyprinus carpio: Changes in glomerular filtration rate,urine and blood properties and plasma catecholamines of carp exposed to hypoxic conditions

• 1.1. Changes in glomerular nitration rate (GFR), urine and blood properties and plasma catecholamines of carp were investigated during and following hypoxia.
• 2.2. GFR and urine flow decreased with increased urinary concentrations of bio-components, except protein, in the course of hypoxia.
• 3.3. Decreases in blood pH, and increases in haematocrit value and plasma K⁺, Ca²⁺, Mg²⁺, inorganic phosphate (P_i), ammonia, lactic acid and catecholamines (CAs) were observed as hypoxia progressed.
• 4.4. Increased GFR and urine flow, and higher values for urinary components, except protein, compared with those of the control were found in the initial post-stress stage.
• 5.5. The possible significance of increased plasma CAs in relation to changes in renal function in hypoxic carp is discussed.

     

Osmoregulation in the brook trout,Salvelinus fontinalis—I. Diel,photoperiod and growth related physiological changes in freshwater

• 1.1. Brook trout (Salvelinus fontinalis) raised from eggs under two photoperiod and two feeding regimes were tested for physiological changes preparatory for transition from freshwater to seawater. Size, age, growth rate, photoperiod, and diel rhythms were examined for possible influences on plasma osmolarity, [Na⁺], [Cl⁻], [K⁺], [Mg²⁺], thyroxine concentration, hematocrit, and gill Na⁺, K⁺-ATPase activity of brook trout in freshwater.
• 2.2. Significant diel cycles were found in plasma osmolarity, [Na⁺] and thyroxine concentration.
• 3.3. Significant size and/or age related changes occurred for plasma osmolarity, Na⁺], [K⁺] and hematocrit, but could explain little of their total variation (0.02 < r² < 0.18).
• 4.4. A sexually dimorphic response to photoperiod was observed in hematocrit for both mature and immature fish, with hematocrit of mature females declining in autumn and hematocrit of immature males increasing in autumn.
• 5.5. Gill Na⁺, K⁺-ATPase activity did not respond to photoperiod or feeding treatment and showed no change with size or age.
• 6.6. Plasma thyroxine levels responded to feeding and photoperiod treatment. There was a significant correlation between the percent mean difference in plasma thyroxine and the mean difference in growth rate between high and low feed fish (r² =0.51), suggesting a relationship between thyroxine and growth.

     

Behaviour and haemolymphatic ionic composition of the intertidal crab Chasmagnathus granulata dana, 1851 (Crustacea: Decapoda) during emersion

• 1.1. Behavioural observations and haemolymphatic measurements of Na⁺ K⁺ and Ca⁺ were performed in Chasmagnalhus granulata during emersion.
• 2.2. Activity levels were found to be higher during voluntary emersion periods than when the animals were submerged. A lt₅₀ of 39.45 hr was observed when no access to water was allowed.
• 3.3. The Na⁺ and K⁺ and Ca⁺ levels increased during aerial exposure. The Na⁺ and K⁺ levels were restored prior the end of the experimental period. Mechanisms for such regulation are therefore discussed. The Ca²⁺ levels, remaining high during emersion, are probably a result of acid-base balance adjustments.

     

Ca2+ - and Mg2+-dependent ATPase activities in the deoxycholate-treated rat heart sarcolemma

• 1.1. Isolated rat heart sarcolemma was treated with different concentrations of an ionic detergent, deoxycholate (DOC) and ATP hydrolysis in the presence of Ca²⁺ or Mg²⁺ was determined.
• 2.2. Both Ca²⁺-dependent ATPase and Mg²⁺-dependent ATPase activities were decreased in the DOC-treated membranes; however, the depression of Mg²⁺-dependent ATPase activity was greater than that of Ca²⁺-dependent ATPase.
• 3.3. The differential changes in Ca²⁺-dependent ATPase and Mg²⁺-dependent ATPase activities were apparent when incubations with DOC were carried out for different time intervals and at different temperatures.
• 4.4. In DOC-treated preparations, the K_m value for Ca²⁺-dependent ATPase was decreased whereas that for Mg²⁺-dependent ATPase was increased. The half maximal velocities of the Ca²⁺-dependent ATPase and Mg²⁺-dependent ATPase enzyme reactions in the treated preparations were obtained at a DOC: membrane protein ratio of 3.0 and 0.6, respectively.
• 5.5. In the DOC-treated membranes exhibiting the half maximal velocities of enzyme reactions, the K_i value for Ca²⁺-dependent ATPase was drastically reduced but remained unchanged for Mg²⁺-dependent ATPase.
• 6.6. The DOC treatment was associated with a loss of protein as well as phospholipids and resulted in changes in the ultrastructural integrity of the membrane.
• 7.7. Varying degrees of decreases in the activities of sarcolemmal adenylate cyclase. (Na⁻-K⁺)-ATPase. 5'-nucleotidase and calcium binding were seen upon DOC treatment.
• 8.8. The extent of reduction in Ca²⁺-dependent ATPase and Mg²⁺-dependent ATPase activities were also different when the membrane was treated with a non-ionic detergent, Lubrol PX.
• 9.9. These data suggest that Ca²⁺-dependent ATPase in heart sarcolemma is more resistant than Mg²⁺-dependent ATPase to detergent treatments and further indicate some differences in the properties of these enzymes.

     

A comparison of the effect of alternating current electronarcosis,rectified current electronarcosis and chemical anaesthesia on the blood physiology of the freshwater bream Oreochromis mossambicus (peters)—III. The effect on the plasma electrolytes Ca2+, Na+ and K+ and on the osmotic pressure of the blood

• 1.1. The effects of alternating current electronarcosis, rectified current electronarcosis and chemical anaesthesia (benzocaine hydrochloride) on plasma electrolytes and on the osmotic pressure of the blood of the freshwater bream Oreochromis mossambicus were evaluated.
• 2.2. Plasma Ca²⁺, Na⁺ and K⁺ concentrations and the osmotic pressure of the blood were monitored over a period of 7 days.
• 3.3. The results showed that the different electrolytes respond differently to the different techniques.
• 4.4. Chemical anaesthesia exhibited the least effects on the parameters studied.

     

Ionic dependence and vanadate sensitivity of (Na+, K+)-ATPase isolated from branchial sac of ascidians

• 1.1. Ion dependence and vanadium-induced inhibition on branchial sac ATPase in five species of ascidian Phlebobranchiata (vanadium-accumulating) and Stolidobranchiata (iron-accumulating) were studied.
• 2.2. The ATPase was obtained from the microsomal fraction, which was prepared from each ascidian branchial sac.
• 3.3. The ATPase was dependent on Mg²⁺ and activated by exogenous Na⁺ + K⁺.
• 4.4. Ouabain inhibited the ATPase activity in vitro, 10 μM to 100 μM vanadate, in vitro, suppressed the (Na⁺, K⁺)-ATPase.

     

Inhibitor of renal gluconeogenesis (IGN): Additional physiological modulator?

• 1.1. A procedure for the partial purification of IGN has been developed: it is insoluble in 80% ethanol but soluble in 6% TCA. It moves in void volume on a column of Sephadex G 25, passes through a membrane with cut-off at 25,000 dallons but not through a membrane with cut-off at 10,000 daltons.
• 2.2. IGN inhibits gluconeogenesis both in kidney cortex and liver slices. The inhibition is small during the first 30 min of incubation but it increases during the following periods of time. Liver slices are much less sensitive to the inhibitory action of IGN than kidney cortex slices.
• 3.3. IGN exerts its effect even in the absence of either K⁺, Ca²⁺ or Mg²⁺ from Krebs-Ringer bicarbonate.

     

Osmolality and electrolyte concentration of hemolymph and the problem of ion and volume regulation of cells in higher insects

• 1.1. The study was carried out on 22 species of insects from 5 orders. The osmolality of their hemolymph varied from 319 to 421 mOsm/kg H₂O, concentration of Na⁺ 4.6 to 118 mM/l, K⁺ 6.3 to 73mM/l, Ca²⁺ 3.6 to 12.9 mM/l, Mg²⁺ 2.3 to 76 mM/l. The most abundant cation in the hemolymph of insects from higher orders is either K⁺ or Mg²⁺.
• 2.2. In the muscles of lower and higher insects K⁺ is usually within 80–120 mM/kg wet wt.
• 3.3. Most Ca²⁺ and Mg²⁺ in hemolymph is bound with protein and low molecular anions, concentration of free Ca²⁺ is 0.9-2.1mM/l Mg²⁺ 3.7–8.0 mM/l.
• 4.4. It is concluded that, in insects, potassium hemolymph, cell volume regulation and accumulation of ions in the cell, are ensured by an increased osmolality of hemolymph due to a high percentage contribution of low molecular organic substances which are retained in the hemolymph due to the absence of filtration apparatus in the Malpighian tubules.