Intracellular pH regulation in ferret ventricular muscle. The role of Na-H exchange and the influence of metabolic substrates.

Abstract

Aspects of pH regulation in ferret ventricular cells have been investigated by using pH- and sodium-selective microelectrodes in bicarbonate-free Tyrode's solution. An acid load was produced by the transient application of NH4Cl (10 or 20 mmol/l). A complete recovery from an acid load was still observed after multiple applications of NH4Cl, but amiloride (0.75 or 1 mmol/l), a blocker of the Na-H exchanger, increased the acidification and inhibited the recovery. Measurements of intracellular sodium concentration showed a transient decrease during the application of NH4Cl and a transient increase above control values during recovery from acidification. This increase was inhibited by amiloride. Intracellular sodium loading (strophanthidin [low calcium-low potassium Tyrode's solution]) did not initially cause an intracellular pH (pHi) change, but the acidification induced by amiloride under those circumstances was larger. Reducing extracellular sodium concentration from 155 to 5 or to 1.5 mmol/l caused an acidification. Changing extracellular pH (pHo) from 6.4 to 8.4 caused an average linear change in pHi in the same direction of 0.085 pHi units/pHo units. The mean intracellular buffering capacity measured with the NH4Cl method and with the proton extrusion mechanism blocked by amiloride was 36 +/- 15 mmol pH-1.l-1 (mean +/- SD), approximately half that of previous estimations. Changing the metabolic substrate from glucose to pyruvate in the superfusing solution caused an acidification of 0.21 pH units. This could be partially blocked by alpha-cyano-4-hydroxycinnamate, a finding consistent with a pyruvate-H+ cotransport and/or a pyruvate-OH- countertransport system being present in ventricular cells. The results of the present study show that ventricular cells can effectively buffer hydrogen ions and that an Na-H exchange system plays a major role in the regulation of pHi.