beta(1) and beta(2)-adrenergic receptor subtype effects in German shepherd dogs with inherited lethal ventricular arrhythmias.

E A Sosunov, R Z Gainullin, N S Moise, S F Steinberg, P Danilo, M R Rosen

Index: Cardiovasc. Res. 48(2) , 211-9, (2000)

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Abstract

Delayed afterdepolarization-induced triggered activity originating in ventricular myocardium is a mechanism for some age-dependent, inherited ventricular tachycardias in a colony of German shepherd dogs.We used standard microelectrode techniques to study beta-adrenergic receptor subtype modulation of the triggered activity in anteroseptal left ventricular myocardium from eleven of these dogs and seven unafflicted, age-matched German shepherd controls.During sustained stimulation at cycle lengths of 300-4000 ms, 10(-9)-10(-7) M isoproterenol concentration-dependently shortened action potential duration (APD) to 90% repolarization more in myocardium from afflicted than from unafflicted dogs. This shortening was prevented by a beta(1)-blocker CGP20712A (10(-7) M) while a beta(2)-blocker ICI118551 (10(-7) M) did not modify the effect of isoproterenol in either group. The beta(2)-agonist zinterol 10(-8)-10(-6) M had no effect on APD. Stimulation at a cycle length of 250 ms in the presence of 10(-7) M isoproterenol induced more triggered AP in myocardium from afflicted than unafflicted dogs. beta(1)-Blockade completely eliminated, while beta(2)-blockade facilitated, and the beta(2)-agonist zinterol did not induce triggered activity in the two groups.Isoproterenol effects on APD and triggered activity in the myocardium of dogs with inherited arrhythmias are due primarily to an abnormality of beta(1)-adrenoceptor mediated signaling that is subject to beta(2)-adrenergic modulation.