Evidence for adenosine receptor-mediated hyperpolarization in coronary smooth muscle

The effects of adenosine and its analogues, 5'-N-ethyl-carboxamidoadenosine (NECA) and 2-chloroadenosine (CAD), were studied on resting membrane potential of bovine coronary artery. The resting membrane potential averaged -51 +/- 1 mV. KCl (50 mM) caused a significant decrease of the resting membrane potential (-30 +/- 1 mV). In separate series of experiments suffusion of the arterial strips with adenosine, NECA, or CAD, at concentrations of 10(-5)M, produced significant increases in resting membrane potential (-68 +/- 1, -80 +/- 2, and -88 +/- 4 mV, respectively). The hyperpolarizing responses to adenosine, NECA, and CAD appeared to have been mediated by an adenosine receptor, since they were blocked by the adenosine receptor antagonist, 8-phenyltheophylline (10(-5) M). The data suggest that activation of an adenosine receptor can result in hyperpolarization of coronary smooth muscle cells.