Possible Relationship between the Release of Calcium Ions and Inactivation of the Potassium Conductance Induced by Noradrenaline in Smooth Muscle of the Guinea-Pig Vas Deferens

Abstract

WAKUI, M. and FUKUSHI, Y. Possible Relationship between the Release of Calcium Ions and Inactivation of the Potassium Conductance Induced by Noradrenaline in Smooth Muscle of the Guinea-Pig Vas Deferens. Tohoku J. exp. Med., 1986, 150 (4), 381-389-In order to examine whether any change in cytoplasmic Ca²⁺ concentration occurs during the noradrenaline (NA)-induced change in the membrane potential, the isometric tension of smooth muscle of the guinea-pig vas deferens was recorded together with membrane potentials using the sucrose-gap method. NA induced a depolarization and an increase in cytoplasmic Ca²⁺ comprising two (initial and second) phases. In time courses, the depolarization and the second phase of the increase in cytoplasmic Ca²⁺ were similar. Only at the phase around the onset of the depolarization, the membrane conductance was increased but then, it was decreased. Lowering the external Ca²⁺ concentration and application of D600 suppressed all of the NA-induced responses. In addition, D600 diminished the size of the NA-induced decrement in the membrane conductance. The present results suggest that the initial phase of the increase in the cytoplasmic Ca²⁺ is due to the influx of Ca²⁺ and the second phase, probably to the release of Ca²⁺ from some intracellular stores. It was discussed that the release of Ca²⁺ might occur at the internal surface of the membrane, and the membrane might be left less permeable to K⁺ as a result.