Summary
Intracellular pH (pHi) regulation was studied in crayfish neurons with pH-, and Na+-sensitive microelectrodes. It was confirmed to involve both a HCO −3 -dependent and a HCO −3 -independent mechanism. The latter was identified as the amiloride-sensitive Na+/H+ exchange described in vertebrate cells. Its dependence on extracellular pH (pHe) and Na+ concentration ([Na+]e) was studied in CO2-free external solutions at 20°C. The steady state pHi and the rate constant (k) of the exponential pHi recovery following an acid load were determined. At pHe=7.5 and [Na+]e=200 mM, the average steady state pHi was 7.09±0.12 (as compared to 7.30±0.10 in the presence of 5 mM bicarbonate). The dependence of the rate constant of recovery on [Na+]e could be described by Michaelis-Menten kinetics; at pHe=7.5 the apparentK m andK max were 39 mM and 1.4 mmol·l−1·min−1, respectively. Decreasing pHe reduced the rate of recovery, the variations ofk with pHe conforming to a simple titration curve with an apparent pK of 7.05±0.21. These kinetic properties of the Na+/H+ exchange in crayfish neurons are similar to those described in vertebrate cells.
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Gaillard, S., Rodeau, J.L. Na+/H+ exchange in crayfish neurons: dependence on extracellular sodium and pH. J Comp Physiol B 157, 435–444 (1987). https://doi.org/10.1007/BF00691827
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DOI: https://doi.org/10.1007/BF00691827