title: The effects of intracellular Na on contraction and intracellular pH in mammalian cardiac muscle.
abstract: Intracellular Na and pH were measured with recessed-tip ion-selective microelectrodes in voltage-clamped sheep cardiac Purkinje fibers. Intracellular Na activity (aiNa) was elevated by inhibiting the Na/K pump. This produced an increase of twitch tension that had a steep dependence on the increase of aiNa. These effects of aiNa on twitch tension are probably mediated by an Na-Ca exchange. An increase of aiNa also produced a component of tonic tension that appears to be produced directly by the Na-Ca exchange. The dependence of tonic tension and aiNa on membrane potential suggests that this exchange process may be voltage-sensitive. The increase of aiNa is associated with an intracellular acidification that appears to be secondary to an increase of [Ca2+]i produced by Na-Ca exchange. Therefore, as well as affecting [Ca2+]i, Na-Ca exchange can under some circumstances influence pHi indirectly, and this complicates the interpretation of changes in tension, since protons and Ca ions have opposite effects on contractile force.
authors.forename: R D
authors.initials: RD
authors.lastname: Vaughan-Jones
authors.forename: D A
authors.initials: DA
authors.lastname: Eisner
authors.forename: W J
authors.initials: WJ
authors.lastname: Lederer
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000378:metabolism; D008564:Membrane Potentials; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D011690:Purkinje Fibers / Q000502:physiology; D012756:Sheep; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D007473:Ion Channels; D012964:Sodium; D002118:Calcium