EFFECT OF CATECHOLAMINES ON INTRACELLULAR PH IN SHEEP CARDIAC PURKINJE-FIBERS

1. It has been reported that catecholamines affect intracellular pH (pH(i)) in a number of tissues, generally by altering the kinetics of the Na+-H+ exchanger. We postulated that catecholamines might affect pH(i) in cardiac tissue. We tested this in resting sheep cardiac Purkinje fibres by measuring transmembrane potential and pH(i) with standard and H+-sensitive microelectrodes. 2. Adrenaline and the beta-adrenergic agonist isoprenaline, both 5.0 x 10(-6) M, resulted in depolarization and intracellular acidification (adrenaline, 0.03 +/- 0.01 pH units, n = 8, P = 0.005; isoprenaline. 0.08 +/- 0.01 pH units, n = 17, P = 0.0001). The alpha-adrenergic agonist phenylephrine, at concentrations up to 200 muM, had no significant effect on membrane potential or pH(i). 3. Isoprenaline significantly attenuated the half-time (t0.5) for pH(i) recovery from intracellular acidification induced via the NH4Cl pulse technique. Isoprenaline also attenuated the hyperpolarization that is normally seen at the onset of pH(i) recovery. Phenylephrine slightly reduced the t0.5 for recovery, although the reduction did not reach statistical significance. 4. Forskolin, 7.5-10 x 10(-5) M, an agent that raises intracellular cyclic adenosine 3',5'-monophosphate (cyclic AMP), also induced depolarization and acidification, similar to that induced by adrenaline and isoprenaline. 5. In the presence of the Na+-H+ exchange blocker 5-dimethyl amiloride, 2-6 x 10(-5) M, isoprenaline-induced acidification was blunted but not abolished. When administered in Na+-free Tyrode solution, isoprenaline-induced acidification was also not abolished. Buffering power, tested using the NH4Cl method, was not decreased by isoprenaline, but rather, was slightly increased. Reversal of H+ driving force across the cell membrane from the normally inward direction to outward (achieved by increasing pH(o) to 8.3-8.5 and depolarizing the membrane with 10 mM K+ solutions) did not prevent intracellular acidification from occurring in the presence of isoprenaline. When glycolysis was inhibited by a 60 min exposure to glucose-free solution containing 5.5 mM 2-deoxyglucose, acidification by isoprenaline was nearly abolished. 6. We conclude that, in resting sheep Purkinje fibres, beta- but not alpha-adrenergic stimulation results in intracellular acidification and depolarization, probably mediated via an increase in cyclic AMP. beta- but no alpha-adrenergic stimulation slows the rate of recovery from intracellular acidification and blunts the hyperpolarization associated with this recovery. 7. The intraeellular acidification appears to be due both to partial inhibition of Na+-H+ exchange and to stimulation of glycolysis by beta-adrenergic agents.