The interactions of protons, calcium and potassium ions on cardiac Purkinje fibres.
1. In sheep Purkinje fibres, acidosis shifts the steady-state current-voltage relation in an inward direction over a wide range of negative potentials. The reversal potential for iK2 is shifted in a positive direction. These changes are consistent with K+ accumulation in the extracellular spaces of the Purkinje fibre. 2. These effects of acidosis are completely prevented by increasing [K]0 from the normal range (2.7--5.4 mM) to 10.8 mM. 3. Increasing [Ca]0 from 2 to 6 mM also produces an inward shift in the steady-state current-voltage relation and a positive shift of the iK2 reversal potential. 4. In 10.8 mM-[K]0 these effects are absent even when [Ca]0 is increased to 20 mM. 5. One possible explanation is that K+ ions may protect the Na pump from inhibition by protons and Ca2+ ions. Alternative explanations are also discussed.
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D006329:Heart Conduction System / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology* / Q000502:physiology; D011690:Purkinje Fibers / Q000187:drug effects / Q000502:physiology*; D012756:Sheep
D011188:Potassium; D002118:Calcium