THE EFFECTS OF VERAPAMIL ON THE CONTRACTION OF RABBIT AORTIC STRIPS

The effects of verapamil (V) on the contraction of rabbit aortic strips induced by KCl and rioradrenaline (NA) were studied. In normal Krebs' solution, the contractions induced by NA were more intensively inhibited by V than those induced by KCl. After the preparations had been exposed for 2 hours to calcium-free solution, the contractile responses to NA decreased more markedly than those to KCl. When V was added to the calcium-free solution, the NA-induced responses were further inhibited, but the KCl-induced responses were not much affected. If the exposure time was shortened to 30 minutes as it is usually done by other authors, KCl-induoed contractions would decrease more than NA. It might be suggested that 30-minute exposure to calcium-free solution only depleted superficially located calcium and 2-hour exposure would also decrease sequestered calcium in the smooth muscle cell. NA mainly utilized sequestered calcium and KCl, superficial one. Verapamil not only inhibited the influx of extracellular calcium, but also had an inhibitory effect on the release of sequestered calcium in the rabbit aortic smooth muscle cells.