pH aspects of transient changes in conduction velocity in isolated heart fibers after partial replacement of chloride with organic anions.

Conduction velocity in isolated rabbit atrial fibers was continuously measured in solutions having a different anionic composition. When 20mmol/l of chloride was replaced by 20 mmol/l lactate or other anions of weak organic acids at constant pH 6.8, biphasic initial transient changes in conduction velocity were observed. The produced transient changes had a greater amplitude with organic acids which have a greater pK and lipid/water partition ratio. The magnitude of the transients was also greater at pH 6.8 than at pH 7.5, and also when the buffering capacity of the superfusion solution was smaller. Measurements of intracellular pH (pHi) in sheep Purkinje fibers and of pH at the surface (pHs) of sheep Purkinje and rabbit atrial fibers with pH sensitive microelectrodes, showed a transient increase of pH and a sustained decrease of pHi on replacement of 20mmol/l chloride by organic anions of weak acids (at constant pH of the superfusion solution). A combined influence of the transient pHs change and the sustained pHi modification seems to be important in the explanation of the biphasic changes in conduction velocity.