Electrophysiological effects of adenosine and adenosine triphosphate on sheep Purkinje fibres under normal and simulated ischaemic conditions.

1. The electrophysiological effects of adenosine and adenosine triphosphate (ATP) were examined in sheep Purkinje fibres, superfused in vitro with either a normal or a hypoxic, hyperkalaemic and acidotic physiological salt solution (PSS). The ability of adenosine to modify the effects of noradrenaline on action potential characteristics was also investigated. 2. The only statistically significant effects of adenosine (10(-6)-10(4) M) and of ATP (10(-6)-10(-4) M) on normal action potential characteristics were a slight dose-dependent shortening of the action potential by adenosine and a depolarization by ATP, 10(-4) M. 3. Superfusion with a hypoxic, hyperkalaemic and acidotic PSS caused marked reductions in resting membrane potential, upstroke and duration of the action potential. 4. Both adenosine and ATP attenuated the reduction in the rate of rise of the upstroke and the amplitude of the action potential caused by the modified PSS. 5. Adenosine did not alter the noradrenaline-induced effects on automaticity or on action potentials of normal or depressed Purkinje fibres. 6. Adenosine and ATP had electrophysiological effects on Purkinje fibres, exposed to conditions in vitro that mimic mild myocardial ischaemia, that were different from those observed on normally polarized fibres.