Ionic selectivity of excitable neurone membrane: Are there any separate potential-dependent channels for Na+,Ca2+, Mg2+?

• 1.1. The dependence of the action potential overshoot and inward currents on ionic concentration has been studied on both intact and completely isolated neurones of Limnaea stagnalis.
• 2.2. The dependence of action potential on ion concentration in the medium is similar to that of intact ones.
• 3.3. The overshoot dependence on the log of Ca²⁺ Mg²⁺ and Na⁺ concentration in the medium is linear. This and the character of inward current dependence on ion concentration allow us to suppose the existence of separate channels for Ca, Na and Mg ions along which they move under the action of their own electrochemical potentials. Conductance of these channels depends slightly on ionic concentration in the medium.
• 4.4. If the medium contains both Ca and Sr ions the overshoot dependence on the log of their concentration is of a non-linear character. This indicates that both these kinds of ions pass through the same channel.
• 5.5. A physiological role of different ion mechanisms of action potential generation is discussed.

     

Examination of water balance and ionic regulation in the earthworm,Eisenia foetida

• 1.1. Weight change after submerging the earthworm into water varied remarkably according to the environmental humidity in which animals were placed before submergence.
• 2.2. Pretreatment with physiological saline solution before submergence in water gave stable values for the ionic concentrations of the body fluid.
• 3.3. Brain removal caused decrease of both sodium and chloride ion concentrations and increase of potassium ion concentration of the coelomic fluid when animals were submerged in water.
• 4.4. Although brain replacement failed, action of a brain hormone is suggested to regulate the decrease of both sodium and choride ions and increase of potassium ion of the coelomic fluid to normal level when animals were submerged in water.

     

Factors regulating the functioning of the in vitro perfused aglomerular kidney of the anglerfish,Lophius piscatorius L.

• 1.1. Kidneys of Lophius were perfused from the renal portal vein with a Ringer's solution.
• 2.2. Mammalian and piscine neurohypophysial hormones (in doses of 20–500 ng/kg body wt) did not affect the rate of urine production or the urinary concentration of inorganic ions.
• 3.3. The rate of urine production and the urinary concentration of magnesium and sodium ions varied with the concentration of magnesium in the perfusate.
• 4.4. The rate of urine production was positively correlated with urine magnesium concentration (r = 0.83 ± 0.04) and negatively correlated with that of sodium (r = −0.40).
• 5.5. The urinary concentration of sodium ions varied inversely with that of magnesium ions (r = −0.89).
• 6.6. Ouabain treatment (0.1–0.8 mM/l) reduced the rate of urine production by over 60% and altered, to varying extents, the pattern of electrolyte excretion. A simple model for the mode of formation of urine by the aglomerular kidney, based on the present results and other observations is suggested.

     

Crayfish retinular cells: Influence of extracellular sodium and calcium upon receptor potential

• 1.1. In crayfish, light stimulation of the retinular cells induces a depolarizing receptor potential.
• 2.2. Experiments were designed to determine the role of Na⁺ and Ca²⁺ on receptor potential during dark And light states.
• 3.3. Depolarization depends on Na⁺ and Ca²⁺ availability to the retinular cell.
• 4.4. Repolarization velocity and response duration depend on extracellular Ca²⁺ availability.
• 5.5. Light adaptation increases receptor potential dependence on calcium and sodium ions.
• 6.6. We analyse these results with respect to other invertebrate photoreceptors.

     

Tetanus responses under rapid bath solution change: Electrotonic depolarization of transverse tubules may release Ca2+ from sarcoplasmic reticulum of Rana japonica skeletal muscle

• 1.1. Single skeletal muscle fibers were transferred from a normal Ringer solution to Na⁺ ion free solution, and vice versa, and tetanus responses were recorded immediately after the transfer.
• 2.2. Fractional tetanus tension recorded immediately after the displacement from the Na⁺ ion free solution to normal Ringer solution was dependent on fiber diameter.
• 3.3. Diffusion of Na⁺ ions along the transverse tubules was simulated [apparent diffusion constant was 3.11 × 10⁻⁶ (cm²/s)].
• 4.4. Our results suggest that the electrotonic spreading of membrane potential, caused by an action potential in the transverse tubules, could release Ca²⁺ ions from sarcoplasmic reticulum.

     

Porphyrin biosynthesis in Rhodopseudomonas palustris—IX. PBG-deaminase. Kinetic studies

• 1.1. PBG-Deaminase obtained from Rp. palustris exhibited classical Michaelis-Menten kinetics in the absence or presence of different ions.
• 2.2. Detailed kinetic studies were carried out in the presence of ammonium, phosphate and magnesium ions.
• 3.3. It has been found that the different effects observed are dependent on both the substrate and the ion concentration.

     

The effects of osmotic stressors on the stenohaline carp (Cyprinus carpio)

• 1.1. Carp were acclimatized to different concentration of urea and mannitol.
• 2.2. The fish survived in 300 mOsm urea and 262 mOsm mannitol for a longer period. Higher concentrations were only tolerated for a short time.
• 3.3. Urea penetrated into the animals. The internal concentration of urea in plasma was nearly equal to the outside concentration after 7 days. Therefore a very high internal osmolality was adjusted (sum of normal and urea osmolality).
• 4.4. Urea treatment only resulted in changes of Ca level, while the concentration of other electrolytes was not clearly varied.
• 5.5. Extracellular space of muscle was reduced while the intracellular space remained unchanged after urea treatment.
• 6.6. Mannitol treatment resulted in changes of electrolyte concentrations due to dehydration.
• 7.7. After 1 day of treatment the concentration of Na in plasma decreased which might indicate the limitation of tolerance.
• 8.8. Immediate shrinkage of ICS and, later, reduction of ECS were clear reactions to mannitol influence.

     

Intracellular calcium in the cells of the outer mantle epithelium of Anodonta cygnea

• 1.1. The intracellular concentration of ionized calcium was measured with double-barrelled ion-sensitive microelectrodes under short-circuit conditions in the isolated outer mantle epithelium of Anodonta cygnea.
• 2.2. When the outside baths contained 1 mmol/1 Ca²⁺ the average intracellular Ca²⁺ was 5.42 ± 0.64 mmol/1(N = 41) while the equilibrium concentration estimated from the intracellular potential measured in the same cells was 5.51 ± 0.33 mmol/l.
• 3.3. Bilateral removal of calcium from the external baths induced a fast fall in the intracellular concentration of this ion by almost three orders of magnitude. This effect was similar to that obtained by removing calcium from the bath on the basolateral side.
• 4.4. Removal of calcium from the bath in contact with the apical side of the preparation had little effect on intracellular calcium.

     

Effects of propionate on the acid microclimate of hen (Gallus domesticus) colonic mucosa

• 1.1. Short-chain fatty acid absorption in hen colon is protonated across the apical border coupled to an apical electrogenic proton pump.
• 2.2. The surface pH of the isolated colonic epithelium was 6.27 ± 0.05, when incubated in Krebs-phosphate buffer pH 7.0.
• 3.3. Propionate 7 and 40mmol/l in the incubation medium (pH 7.0) increased microclimate pH to 6.47 ± 0.04 and 6.56 ± 0.04. Inhibition of metabolic activity by potassium cyanide 1 mmol/1 increased surface pH to 6.66 ± 0.06.
• 4.4. The calculated concentration of propionic acid in the microclimate is near-linearly related to the propionate concentration. Thus, the acid microclimate is not responsible for the Michaelis-Menten like kinetics of propionate transport.

     

Uptake of inorganic ions from the maternal circulation during development of the embryo of a viviparous lizard,Sphenomorphus quoyii

• 1.1. Inorganic ion content of developing follicles and of whole eggs and separated embryos and yolk sacs of the viviparous lizard, Sphenomorphus quoyii has been measured.
• 2.2. There is a net increase in calcium, sodium and potassium in whole eggs during gestation. Magnesium and phosphorus content remains constant.
• 3.3. The additional ions are incorporated into the developing embryo.
• 4.4. Calcium content of the yolk is compared with that of the fowl and other species of reptile.

     

In vivo photo-affinity labelling of glutathione receptors mediating the tentacle ball formation,a behavioral response associated with the feeding of Hydra

• 1.1. The tentacle ball formation, a response associated with the feeding of Hydra japonica, with S-(p-azidophenacyl)-glutathione (GSPAP) was reduced upon illumination.
• 2.2. GSPAP did not cause the depression without illumination nor did illumination without GSPAP.
• 3.3. The concentration dependence of the response of the photolabelled animals suggested high and low affinity glutathione receptors. The low affinity receptor may be efficiently tagged with GSPAP upon photolysis.

     

Ion-exchange phenomena regulate the environment of embryos in the eggs of freshwater fish

• 1.1. Calcium-selective microelectrodes have been used to measure the activity of calcium in the perivitelline fluid of brown trout eggs, exposed to water with a range of Ca²⁺ concentrations. Trans-chorion potential differences were also measured.
• 2.2. These values are compared with those predicted by a model based on ion-exchange theory and the Donnan equilibrium. The model allows for partial-dissociation of acid-groups in both the perivitelline fluid and the chorion, and the effects of external pH and ion concentration on this dissociation. The ion-exchange properties of perivitelline fluid and chorion were determined by acid-base titration.
• 3.3. The model has the potential to predict the effects of external pH and ion concentration on the distribution of many ions in fish eggs; especially in nutrient-poor waters. It is particularly relevant, therefore, to studies of acidification and metal pollution.

     

Whole-cell outward currents in freshly dissociated rat placental cells

• 1.1.We applied whole cell voltage clamp techniques to freshly dissociated rat placental cells (20–21 days gestation). Tetraethylammonium (TEA)-sensitive outward currents were recorded in about 50% of cells.
• 2.2.The outward current had a reversal potential of -50mV which is more positive than the potassium equilibrium potential (−82mV).
• 3.3.The bath solution without NaCI decreased the outward current amplitude, while the elimination of only Na ions from the bath solution did not modify the outward current.
• 4.4.The results suggest a possible contribution of chloride ions to the outward currents in rat placental cells.

     

Internal reference standards in ionic regulation and the predictability of ionic concentrations in animals

• 1.1. The regulation of ions at similar concentrations in most individuals of a species suggests the existence of internal reference standards.
• 2.2. Few have been identified, but many probably relate to cell membrane properties, including potentials, surface charge densities and equilibrium constants of receptor molecules.
• 3.3. Solubility may sometimes determine the product [Ca²⁺][CO₃²⁻].
• 4.4. Reference standards must generally each relate to more than one ionic species.
• 5.5. For some concentrations, including osmolality, there may be no direct reference standard.

     

Cationic and anionic channels of apical receptive membrane in a taste cell contribute to generation of salt-induced receptor potential

• 1.1. After ionic composition of superficial fluid (ISF) and interstitial fluid (ISF) of the frog Rana catesbeiana) tongue had mostly been changed with a low Na⁺ saline solution, the relations between membrane potentials and receptor potentials in a frog taste cell evoked by various concentrations of NaCl and various types of salts were analyzed to examine permeability of the taste receptive membrane to cations and anions.
• 2.2. The mean reversal potentials for depolarizing potentials of a taste cell in response to 0.05 M, 0.2 M and 0.5 M Nad were -40.0, 6.4 and 28.8 mV, respectively.
• 3.3. When adding an anion channel blocker, SITS, to a NaCl solution the reversal potential for receptor potential with NaCl plus SITS became about twice as large than with NaCl alone.
• 4.4. Reversal potentials for 0.2 M NaCl, LiCl, KCl and NaSCN were 6.4, 25.4, −1.0 and −7.8 mV, respectively, indicating that permeability of the apical taste receptive membrane to cations of Cl⁻ salts is arranged in the order of Li⁺ > Na⁺ > K⁺ and that the permeability to anions of Na⁺ salts is arranged as SCN⁻ > Cl⁻
• 5.5. It is concluded that in the case of NaCl stimulation, Na⁺ and Cl⁻ of NaCl stimulus permeate NaCl-gated cationic and anionic channels at the apical taste receptive membrane in generating receptor potentials.

     

Water loss and haemolymph osmolarity of Potamon potamios,an aquatic land crab,under stress of dehydration and salinity

• 1.1. Small crabs survived over 18% water loss and large crabs 21% when in dry air. Size, temperature and relative humidity affected this rate.
• 2.2. Haemolymph osmolarity of newly collected crabs ranged from 530 to 630 mOsm/kg, depending on their size and the season.
• 3.3. When dehydrated, haemolymph osmolarity rose to over 700 mOsm/kg, and ion concentration increased by over 10%.
• 4.4. Crabs survived in sea-water for at least two weeks. Haemolymph osmolarity rose and ion concentration increased. The acclimation pattern affected the haemolymph osmolarity.

     

Adenosine triphosphate as a determinant of magnesium levels in cytoplasm

• 1.1. Levels of free magnesium ion in various tissues are reviewed.
• 2.2. Total magnesium and ATP levels in different tissues are correlated, due to the presence of MgATP.
• 3.3. Relationships between pH and temperature in poikilotherms are such as to keep constant the amount of magnesium bound by ATP.
• 4.4. ATP hydrolysis in vivo generally tends to release magnesium ions, but conditions in some muscle may be such as to minimize this release.

     

Vanadium inhibition of human parietal lobe ATPases

In vitro influence of vanadate and vanadyl ions on the activities of Na,K- and Ca,Mg-ATPase from synaptosomal membranes of the parietal lobe of the human brain were compared.

• 1.1. Vanadate and vanadyl inhibit the enzymes activities in the investigated fraction.
• 2.2. Vanadate is a more effective inhibitor of both ATPases in the concentrations above 50 μM and vanadyl is an effective inhibitor in a very low concentration (10 nM).
• 3.3. Vanadate seems to be an uncompetitive inhibitor of Na,K-ATPase (k₁ = 880 nM).

     

Ontogeny of a circadian rhythm in the glycaemic response of Gallus domesticus to glucagon

• 1.1. A circadian rhythm in the glucagon-mediated glycogenolytic response was absent in the newly-hatched chick but was present in the bird aged 1 week.
• 2.2. The peak glucose concentration was 38% higher in the afternoon in 1-week-old birds and 50% in 2-week-old birds.
• 3.3. The circadian rhythm was not present in 1-week-old birds subjected to constant illumination from hatching.
• 4.4. Starving the bird reduced the response to glucagon, irrespective of the time of day.

     

Seasonal changes of water,electrolytes and aldosterone levels in blood serum,brain and kidney of the Egyptian cobra “Naja haje haje”

 

• 1.The levels of water, Na, K, Ca and Mg in blood serum, brain and kidney and aldosterone level in blood of Naja haje haje were studied during the different phases of the annual cycle.
• 2.The water content in the tissues studied displayed only minor changes as the animals passed from one phase to the other.
• 3.A significant increase in Na was recorded in the brain during the different phases indicating a depressed sodium pump, whereas the blood Na level showed a significant decrease during hibernation.
• 4.K increased in blood serum, brain and kidney during hibernation, while a nonsignificant decrease was found in blood serum during arousal. The brain may act as a potassium reservoir.
• 5.An increase in Ca and Mg concentration was recorded in blood serum, brain and kidney during prehibernation and hibernation. The data suggested a homeostatic function in the transport and metabolism of these cations.
• 6.Aldosterone exhibited a highly significant decrease especially during hibernation. The aldosterone regulation of ionic composition is discussed.
• 7.Na/K and Ca/Mg ratios in the brain may explain the decreased excitability during winter torpor.