Dependence of Sodium-Calcium Exchange Current Through the Membrane of Salivary Gland Cells of Chironomus on pH of the Extracellular Solution (original) (raw)
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Journal of General Physiology, 1988
Ion-sensitive microelectrodes and current-voltage analysis were used to study intracellular pH (pH3 regulation and its effects on ionic conductances in the isolated epithelium of frog skin. We show that pHi recovery after an acid load is dependent on the operation of an amiloride-sensitive Na+/H + exchanger localized at the basolateral cell membranes. The antiporter is not quiescent at physiological pHi (7.1-7.4) and, thus, contributes to the maintenance of steady state pHi. Moreover, intracellular sodium ion activity is also controlled in part by Na § uptake via the exchanger.
Journal of Clinical Investigation, 1995
The purpose of this study was to define the mechanism whereby agonists that increase free cytosolic calcium (Ca,2+) affect intracellular pH (pH1) in smooth muscle. Rat aortic vascular smooth muscle cells grown on coverslips were loaded with BCECF/AM or fura-2/AM for continuous monitoring of pHi or Ca,2+, respectively, in a HCO3/CO2containing medium. Recovery from rapid increases in Cal2+ produced by 1 juM angiotensin (Ang) II (A Ca,2+-229±43 nM) or 1 pzM ionomycin (A Ca,-`-148±19 nM) was accompanied by a fall in pH' (A pH,,-0.064±0.0085 P < 0.01, and-0.05±0.012 pH units, P < 0.01, respectively). Neither the fall in pH, nor the rise in Ca,2' elicited by Ang II was prevented by pretreatment with agents which block the action of this agonist on pH, via the stimulation of the ClI HC03 exchangers (DIDS, 50 jM) or the NaI/H+ antiporter (EIPA, 50 ,uM). In the presence of DIDS and ELPA, Ang II produced a fall in pHi (A pH.,-0.050+0.014, P < 0.01) and a rise in Ca,2+ (A Ca2' 252±157 nM, P < 0.01). That the change in pH; was secondary to changes in Cal2+ was inferred from the finding that, when the rise in Ca,2' elicited by Ang II was prevented by preincubation with a Ca2+ buffer, BAPTA (60 jLM), the fall in pH, was abolished as well (A pHj, 0.0014±0.0046). The pH, fall produced by Ang II and ionomycin was prevented by cadmium at a very low concentration (20 nM) which is known to inhibit plasma membrane Ca2+-ATPase activity (A pH,-0.002±0.0006 and-0.0016 pH units, respectively). Cadmium also blunted Ca,2+ recovery after Ang II and ionomycin. These findings suggest that the fall in pH, produced by these agents is due to H+ entry coupled to Ca2+ extrusion via the plasma membrane Ca2+-ATPase. Our results indicate that agonists that increase Ca,2+ cause intracellular acidification as a result of Ca2+/H+ exchange across the plasma membrane.
Modulation of Ca 2+ Influx in Leech Retzius Neurons. I. Effect of Extracellular pH
Journal of Membrane Biology, 2001
We investigated the cytosolic free calcium concentration ([Ca 2+ ] i ) of leech Retzius neurons in situ while varying the extracellular Ca 2+ concentration via the bathing solution ([Ca 2+ ] B ). Changing [Ca 2+ ] B had only an effect on [Ca 2+ ] i if the cells were depolarized by raising the extracellular K + concentration. Surprisingly, raising [Ca 2+ ] B from 2 to 10 mM caused a decrease in [Ca 2+ ] i , and an increase was evoked by reducing [Ca 2+ ] B to 0.1 mM. These changes were not due to shifts in membrane potential. At low [Ca 2+ ] B moderate membrane depolarizations were sufficient to evoke a [Ca 2+ ] i increase, while progressively larger depolarizations were necessary at higher [Ca 2+ ] B . The changes in the relationship between [Ca 2+ ] i and membrane potential upon varying [Ca 2+ ] B could be reversed by changing extracellular pH. We conclude that [Ca 2+ ] B affects [Ca 2+ ] i by modulating Ca 2+ influx through voltage-dependent Ca 2+ channels via the electrochemical Ca 2+ gradient and the surface potential at the extracellular side of the plasma membrane. These two parameters are affected in a counteracting way: Raising the extracellular Ca 2+ concentration enhances the electrochemical Ca 2+ gradient and hence Ca 2+ influx, but it attenuates Ca 2+ channel activity by shifting the extracellular surface potential to the positive direction, and vice versa.
Experimental Brain Research, 1994
The influence of changes in intra-and extracellular pH (pHi and pile, respectively) on the cytosolic, free calcium concentration ([Ca2+] 0 of neocortical neurons was studied by microspectrofluorometric techniques and the fluorophore fura-2. When, at constant pile, pH i was lowered with the NH4C1 prepulse technique, or by a transient increase in CO2 tension, [Ca2+]i invariably increased, the magnitude of the rise being proportional to ApHi. Since similar results were obtained in Ca2+-free solutions, the results suggest that the rise in [Ca2 § was due to calcium release from intracellular stores. The initial alkaline transient during NH4C1 exposure was associated with a rise in [Ca2+]i. However, this rise seemed to reflect influx of Ca 2+ from the external solution. Thus, in Ca2+-free solution NHgC1 exposure led to a decrease in [Ca2+]~. This result and others suggest that, at constant pile, intracellular alkalosis reduces [Ca2+]i, probably by enhancing sequestration of calcium. When cells were exposed to a CO2 transient at reduced pHi, Ca 2 § rose initially but then fell, often below basal values. Similar results were obtained when extracellular HCO 3concentration was reduced at constant CO2 tension. Unexpectedly, such results were obtained only in Ca2+-containing solutions. In Ca2+-free solutions, acidosis always raised [Ca2 § It is suggested that a lowering of pHe stimulates extrusion of Ca 2+ by ATP-driven Ca2+/2H § antiport.
Intracellular pH changes induced by injection of cyclic nucleotides into gastropod neurones
The Journal of Physiology, 1984
1. Injections of cyclic AMP (cAMP) or cyclic GMP (cGMP) into identifiable gastropod neurones under voltage clamp induced reversible cytoplasmic pH changes which were measured using the indicator dye Arsenazo III and pH micro-electrodes. Similar injections of 5AMP or 5'GMP did not induce such effects. 2. In about one-half of the population of neurones examined, cAMP injections (0-1-10 mM) induced pH decreases with latencies of 1-5 min and maximum response times 12-25 min post-injection. Comparable injections of cGMP into these cells resulted in decreases with latencies less than 1 min and maximum response times 5-10 min. The amplitude and duration of these pHi decreases were dose dependent. 3. In the other half of the population of neurones tested, cAMP injection induced an immediate alkalinization lasting 5-10 min followed by an acidification which displayed a maximum response time within the same range as those in the first group. cGMP injection into these cells induced only acidifications with faster peak responses than with cAMP. Since cGMP did not elicit alkalinizing responses, the slower response time of the first group of cells with cAMP may reflect an always present underlying alkalinization. 4. The nucleotide-induced acidification was potentiated in neurones bathed in the phosphodiesterase inhibitor IBMX. Injections of non-hydrolysable cAMP analogues also induced acidifications which were longer lasting than comparable doses of cyclic AMP. These results indicate that the elevated [H+]i was not simply due to hydrolysis of the injected cyclic nucleotide. 5. The pHi changes were invariably of much longer duration than a nucleotideinduced inward current (Connor & Hockberger, 1984) and persisted in Na-free salines which eliminated the current response. These results support the notion that cyclic nucleotide elevation can affect cellular metabolic processes distinct from effects on ion transport mechanisms.
Ionic dependence of the resting membrane potential of rabbit lacrimal gland in vitro
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1977
1. Intracellular measurements of membrane potentials were made from acinar cells of rabbit lacrimal gland in vitro at 25 + 0.3°C (-+ S.E.) by using 3 M KCl-filled glass microelectrodes. 2. The mean resting membrane potential in a Krebs-Ringer bicarbonate solution was-26.7-+ 0.3 mV, inside the cell negative. 3. Elevation of the external K ÷ concentration ([K ~] 0) caused depolarization of the resting potential. When [K ÷] 0 was above 5 raM, a tenfold increase in [K ÷] 0 decreased the membrane potential by approx. 15 mV. This depolarization was not mediated by the release of acetylcholine (ACh) from the depolarized nerve terminals since it was seen in the presence of 10-s M atropine. 4. Equimolar replacement of [Na ÷] 0 by either choline or Tris at constant [K ÷] 0 (5.8 raM) produced hyperpolarization. The resting potential was-33.1 + 0.6 mV and-38.9-+ 0.6 mV, when 70 mM [Na ÷] 0 was replaced by choline and Tris respectively. 5. The resting potential was not affected by either partial or complete substitution of [C1-] 0 with SO~-6. Omission of Ca:* from the external medium in the absence and in the presence of 5 mM EGTA decreased the membrane potential by 5.4 rnV and 11.8 mV respectively. 7. It is concluded that the resting membrane potential of rabbit lacrimal gland is independent of the external C1-but it primarily depends on the external Na ÷, K ÷ and Ca :+. The data were interpreted in terms of high membrane permeability to Na ÷ and K ÷ of the lacrimal gland cells. The relative permeability ratio, PNa/PK, in normal Krebs-Ringer bicarbonate solution was estimated to be 0.35.
K-induced alkalinization in all cell types of rabbit gastric glands: A novel K/H exchange mechanism
The Journal of Membrane Biology, 1992
Digital image processing of the pH-sensitive dye BCECF was used to examine the effects of high [K] media on cytoplasmic pH (pHi) of individual cells within isolated rabbit gastric glands. When cells were acidified to pH i 6.5 from the resting pH~ of 7.2-7.3 and then exposed to solution containing 77 mM K plus amiloride (to block Na/H exchange), recovery to phi 7.0 was observed. This K-induced alkalinization occurred in all cell types of the gland, including cells within antral glands that were devoid of parietal cells (PC). This process was independent of extracellular Na and CI and was unaffected by: 5 mMBa or 200 /xM bumetanide, or acute treatment with either 500/*M ouabain or 100 poM cimetidine, histamine or carbachol. SCH28080, which inhibits the PC H/K-ATPase when used in the low/*M range of concentrations, blocked the K effect on phi at 100/*M but was ineffective at 1 /xM. A similar pH i recovery was also stimulated by Li, Cs (both 72 raM), and TI (10 mM), in the order Li > K > Cs > TI (all in the presence of amiloride), and these alkalinizations were also blocked by 100 p~M SCH28080. Parallel experiments were performed to test the effect of these ions on 14[C]-aminopyrine accumulation, an index of acid secretion by the H/K-ATPase at the lumenal membrane of the PC. There was no correlation between the rates of cation-induced pH i recovery from an acid load and H secretion as measured by the accumulation of aminopyrine. We conclude that the K-(and Cs-and Li-) dependent pH i recovery is mediated by a novel cation/H exchange mechanism that is distinct from the PC H/K-ATPase.
Methodical approaches to identification of transmembrane current of sodium-calcium exchange
Neurophysiology, 1998
The methodical approaches allowing one to record transmembrane currents related to coupled Na+-Ca 2+ exchange through the cell membrane are considered. The techniqueS are based either upon changes of the Na + or/and Ca 2+ concentration gradients, or upon shifts of the membrane potential. The advantages and disadvantages of these techniques applied to different objects, as well as the authors' own experiments on secretory cells of the salivary glands of Chironomus larvae, are discussed.
The pH Dependency of Relative Ion Permeabilities in the Crayfish Giant Axon
Biophysical Journal, 1969
The dependence of the membrane potential on potassium, chloride, and sodium ions, was determined at the pH's of 6.0, 7.5, and 9.0 for the resting and depolarized crayfish ventral nerve cord giant axon. In normal saline (external potassium = 5.4 mM), the dependence of the membrane potential on the external potassium ions decreased with lowered pH while that for chloride increased. In contrast, in the potassium depolarized axon (external potassium = 25 mM), the dependence of the membrane potential on external potassium was minimum around pH 7.5 and increased in either more acidic or basic pH. In addition, the dependence of the membrane potential on external chloride in the depolarized axon was maximum at pH 7.5 and decreased in either more acidic or basic pH. The sodium dependency of the membrane potential was small and relatively unaffected by pH or depolarization. The data are interpreted as indicating a reversible surface membrane protein-phospholipid conformation change which occurs in the transition from the resting to the depolarized axon.