Electrophysiological and functional effects of adenosine on ventricular myocytes of various mammalian species.

The goal of this study was to determine the electrophysiological and functional effects of adenosine on ventricular myocytes of guinea pig, rabbit, rat, and ferret hearts. Adenosine (100 microM) shortened the action potential durations of rat and ferret myocytes by 14 +/- 1 and 57 +/- 7%, reduced the amplitudes of cell twitch shortening by 13 +/- 1 and 54 +/- 5%, and increased outward currents by 15 +/- 4 and 55 +/- 5%, respectively, but had no effect on guinea pig and rabbit myocytes. The properties of adenosine-activated outward current in rat and ferret ventricular myocytes indicated that this current is the adenosine-sensitive K+ current [IK(Ado)]. Adenosine had no significant effect on basal Ca2+ current but specifically inhibited isoproterenol-stimulated L-type Ca2+ current in myocytes of all species studied. Binding studies revealed that the density of A1 adenosine receptors (A1AdoR) was highest in ferret and lowest in rabbit myocytes, but the differential effects of adenosine among species could not be solely explained by differences in A1AdoR density. In summary, adenosine shortened the action potential and reduced the twitch shortening of rat and ferret but not of guinea pig and rabbit ventricular myocytes. Shortening of the action potential was associated with the activation of IK(Ado). The anti-beta-adrenergic action of adenosine appeared to be independent of species.