Adenosine attenuation of the electrophysiological effects of isoproterenol on canine cardiac Purkinje fibers.

Adenosine is known to have effects on electrophysiologic parameters of the sinus node, AV node and atrium and to antagonize isoproterenol-induced increased inotropy in the ventricle. However, the effects on cardiac Purkinje fibers are not well established. Therefore, the purpose of the present experiments was to examine the effects of adenosine alone and adenosine on isoproterenol-treated canine cardiac Purkinje fibers. Microelectrode techniques were used to record transmembrane action potentials. Adenosine alone (10(-7) to 10(-4) M) produced no effects on action potential characteristics of paced fibers. Adenosine in concentrations of 10(-7), 10(-6), 10(-5) and 10(-4) M produced a 15, 24, 44* and 72*% attenuation of isoproterenol (10(-6) M)-induced action potential duration shortening, respectively (*P less than .001). In 7 of 7 fibers depolarized with 22 mM K+, adenosine (10(-4) M) ablated calcium-dependent action potentials restored with isoproterenol (10(-6) M). These effects were antagonized by theophylline (5 X 10(-5) M) and adenosine deaminase (1 U/ml). Action potential shortening due to superfusion of high calcium Tyrode's solution and calcium-dependent action potentials generated in Na+ free-high Ca++ Tyrode's solution were not antagonized by adenosine. Adenosine (10(-5) M) produced a negative chronotropic effect, increasing escape intervals from 2669 +/- 647 to 3702 +/- 717** msec in control fibers and from 1864 +/- 329 to 2658 +/- 399** msec in tyramine (10(-4) M)-treated fibers (**P less than .05), but failed to produce a negative chronotropic response in fibers pretreated with propranolol (10(-7) M).(ABSTRACT TRUNCATED AT 250 WORDS)