EFFECTS OF H2O2 ON MEMBRANE-POTENTIAL AND [CA2+](I) OF CULTURED RAT ARTERIAL SMOOTH-MUSCLE CELLS

The effect of 1 mmol/l H2O2 was studied on the membrane potential and [Ca2+](i) with microelectrodes and the fura-2 technique, respectively. H2O2 induced a biphasic increase in [Ca2+](i) with a fast transient peak and a subsequent plateau. H2O2 also led to a biphasic hyperpolarization of the cells with a similar time course. This was followed by a slight depolarization after wash-out of H2O2 External Ca2+ free solutions and treatment with the Ca2+ ionophore A23187 (1 mu mol/l) abolished the effect of H2O2 on [Ca2+](i) and almost entirely reduced the effect on the membrane potential. Phenylephrine (10 mu mol/l) or A23187 also induced very similar biphasic hyperpolarizations of the membrane as H2O2 which were fully reversible after wash-out. It is concluded that H2O2 hyperpolarizes the membrane by opening of Ca2+ dependent K+ channels. (C) 1995 Academic Press, Inc.