VANADATE-INDUCED POTENTIATION OF SMOOTH-MUSCLE CONTRACTILITY IN THE RAT DEPOLARIZED UTERUS

The effect of ortho-vanadate on Ca2+-influx in the uterine smooth musc le was investigated. Orthovanadate (10 - 300 mu M) gradually increased the muscular tone of rat isolated uterus bathed in a high K+ (30 mM) - low Ca2+ (0.15 mM) solution. This response was blocked by nifedipine (10 nM) and reproduced by BAY K 8644 (3 - 300 mM). Atropine and indom ethacin were unable to block the effects induced by vanadate and BAY K 8644. Cumulative addition of CaCl2 to the tissue bathed in a depolari zed solution without CaCl2 produced a graded tonic response that was p otentiated by either vanadate (30 mu M) or BAY K 8644 (30 nM), and inh ibited by nifedipine, Neither vanadate (30 mu M) nor BAY K 8644 (30 nM ) modified the uterine tone of tissues immersed in the depolarizing so lution without CaCl2. It is concluded that vanadate-induced contractio n of rat uterine smooth muscle involves Ca2+-influx from the extracell ular medium to the myometrial cell. Vanadate might act as a Ca2+-chann el activator, similar to BAY K 8644.