title: Intracellular pH in depolarized cardiac Purkinje strands.
abstract: In isolated sheep cardiac Purkinje strands the effect of membrane depolarization on intracellular pH (pHi) and on pHi changes produced by addition and withdrawal of NH4+ and Co2/HCO3- was investigated. pHi was continuously measured with double-barreled glass microelectrodes. Repetitive stimulation at high rate resulted in a moderate intracellular acidification (approximately 0.03 pH unit after a 3 Hz train of 2 min), whereafter pHi returned toward its pre-stimulus level. Prolonged depolarization, evoked either by current injection or by superfusion with high K+ solutions, was accompanied by a small acid shift. In the depolarized cell, addition of NH4+ to the superfusate caused intracellular alkalinization followed by re-acidification which was slower than at normal membrane potential. Following intracellular acidification caused by withdrawal of NH4+, pHi recovery also was slightly slower than in the normally polarized cell. In the depolarized fiber, removal and readdition of CO2/HCO3- produced the expected intracellular alkalinization and acidification respectively. Recovery from CO2-induced acidosis was slowed somewhat in high K+ (low Na+) superfused fibers, not in current depolarized fibers. In the depolarized cell, steady state pHi in CO2/HCO3- containing and in CO2/HCO3- free solution tended to become identical. These experiments support the hypothesis that in the normally polarized Purkinje fiber passive shuttle movement of NH4+/NH3 and CO2/HCO3- occurs and could perhaps at least be partly responsible for the lower steady state pHi as compared to that reached in NH4+-free and CO2/HCO3- -free solutions respectively.
mesh_terms: D000641:Ammonia / Q000378:metabolism; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D001693:Biological Transport, Active; D002245:Carbon Dioxide / Q000378:metabolism; D002463:Cell Membrane Permeability; D006329:Heart Conduction System / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials; D008839:Microelectrodes; D011690:Purkinje Fibers / Q000378:metabolism*; D012756:Sheep
chemical_list: D001639:Bicarbonates; D002245:Carbon Dioxide; D000641:Ammonia