Agonist-Induced Activation of Rat Mesenteric Resistance Vessels: Comparison Between Noradrenaline and Vasopressin

The effects of noradrenaline (NA, 10 M) and [arginine]vasopressin (AVP, 10 M) on tension in Ca -free medium and on membrane potential, and the inhibition of NA- and AVP-induced contractions by isradipine, have been compared in mesenteric resistance vessels (MRVs) from Wistar–Kyoto (WKY) rats. The release of intracellular Ca by AVP contributed significantly less to its tension development than does that by NA. Nonetheless, the concentration-response curves for inhibition by isradipine of NA- and AVP-induced tonic tension were nearly identical. Similarly, these two agonists produced the same degree of membrane depolarization. In addition, both agonists were able to stimulate large contractions in vessels previously depolarized by 80 mM K. AVP also stimulated Ca influx into rat cultured aortic smooth muscle cells. In contrast to the stimulation of Ca influx by KCI depolarization, the agonist-stimulated Ca influx was insensitive to inhibition by organic Ca antagonists. It is concluded that Cap+ entry through receptor-operated Ca -permeable channels (ROCs) may contribute to agonist-induced activation of rat aortic and MRV smooth muscle.