[Effect of noradrenaline and potassium ions on the electrical and contractile activity of coronary artery smooth muscle cells].

Smooth muscle cells (SMC) of circular strips from bovine and pig left descending anterior arteries responded to the increase of external potassium concentration from 5.9 to 160 mM with depolarization of the SMC membrane. At IK+I0 up to 40 mM this depolarization entailed relaxation of the strips; at IK+I0 from 40 mM to 80 mM the tonic contraction occurred. An increase of external potassium concentration up to 160 mM led to depolarization of the SMC membrane preceded by the AP. These changes were accompanied by initial phasic and subsequent tonic (potassium contracture) contractions. Noradrenaline (10(-5) M) added to the bathing solution induced membrane hyperpolarization and relaxation of the SMC, or relaxation without substantial shifts of the membrane potential level.