CHARACTERISTICS OF CA INFLUXES THROUGH VOLTAGE-OPERATED AND RECEPTOR-OPERATED CA CHANNELS IN UTERINE SMOOTH-MUSCLE

Abstract

The characteristics of Ca channels in isolated uterine smooth muscles from estradiol-treated ovariectomized rats were investigated. When the muscles were preincubated in Ca-depleted Ringer''s solution for .apprx. 60 min and then immersed in Ca-depleted high K Ringer''s solution or treated with acetylcholine (ACh) and serotonin (5-HT), no contractile response was observed. In both cases when CaCl2 was then added, a contractile response was induced. The contractile responses induced by KCl, ACh and 5-HT were inhibited dose-dependently by Ca antagonists [CoCl2, verapamil, diltiazem, atropine and ketanserin] and these inhibitions were counteracted competitively by an increase in the concentration of CaCl2. The characteristics of KCl-, ACh- and 5-HT-stimulated 45Ca uptake were investigated under the same conditions as the contractile responses. The contractile responses to high KCl, ACh and 5-HT induced by addition of CaCl2 in Ca-depleted Ringer''s solution were dependent upon influx of Ca ions into uterine smooth muscle cells.