Regulation of intracellular pH in sheep cardiac Purkinje fibre: interactions among Na+, H+, and Ca2+1.

Journal article

Experiments were performed on sheep cardiac Purkinje fibres using pH- and sodium-selective microelectrodes, while simultaneously measuring tension, to determine if the fall in intracellular pH (pHi) following a rise in intracellular Na+ activity (aiNa) is caused by inhibition or reversal of acid extrusion on Na+-H+ exchange. A rise in aiNa was induced either by using the cardioactive steroid strophanthidin to inhibit the sarcolemmal Na+-K+ pump or by increasing the frequency of stimulation (0-4 Hz). Both of these manoeuvres led to an increase in aiNa and a decrease in pHi. Following exposure to strophanthidin, amiloride (an inhibitor of sarcolemmal Na+-H+ exchange) produced a decrease in both pHi and aiNa. These effects of amiloride increased with decreasing pHi, indicating that acid extrusion on Na+-H+ exchange is stimulated by the fall in pHi. The changes in intracellular Na+ and H+ caused by amiloride were quantitatively consistent with an electroneutral stoichiometry. The fall in pHi during strophanthidin exposure is therefore not caused by inhibition or reversal of acid extrusion Na+-H+ exchange. It is likely that the fall in pHi during a rate increase is also independent of Na+-H+ exchange. This is because (i) it has been shown previously to occur in the presence of amiloride and (ii) the calcium antagonist D600 completely abolished the stimulation-dependent fall in pHi. It is concluded that the intracellular acidosis following inhibition of the sarcolemmal Na+-K+ pump or following an increase in the rate of stimulation is secondary to a rise in intracellular calcium.

Authors: Kaila, K; Vaughan-Jones, R; Bountra, C

• Publication status: Published
• Journal: Canadian journal of physiology and pharmacology
• Volume: 65
• Issue: 5
• Pages: 963-969
• Publication date: 1987-05-01
• DOI: 10.1139/y87-153
• EISSN: 1205-7541
• ISSN: 0008-4212
• Language: English
• Keywords: Strophanthidin; Body Fluids; Microelectrodes; Calcium; Purkinje Fibers; Membrane Potentials; Amiloride; Ammonium Chloride; Intracellular Fluid; Heart Conduction System; Electric Stimulation; Sheep; Animals; Sodium; Hydrogen-Ion Concentration