THE EFFECTS OF ALPHA-ADRENOCEPTOR AGONISTS ON INTRACELLULAR CA-2-MUSCLE CELLS FROM RAT TAIL ARTERY( LEVELS IN FRESHLY DISPERSED SINGLE SMOOTH)

1 The presence of functional alpha-adrenoceptors in freshly dispersed single smooth muscle cells from rat tail arteries was investigated by use of selective alpha-adrenoceptor agonists and antagonists. 2 Cirazo line, a selective alpha1-adrenoceptor agonist, caused a prazosin-sensi tive, rapid but transient increase in intracellular Ca2+, Which was pa rtially inhibited by the voltage-dependent Ca2+ channel blocker, nifed ipine. 3 TL99, an alpha2-adrenoceptor agonist, in the presence of praz osin, initiated a slow and sustained increase in intracellular Ca2+ Wh ich was partially inhibited by yohimbine and almost completely blocked by nifedipine. 4 In rat tail artery, the effects (dose-response and t ime-response curves) of cirazoline and TL99 on intracellular Ca2+ leve ls in freshly dispersed single smooth muscle cells were comparable wit h those obtained with organ bath studies of ring preparations of arter y. 5 In freshly dispersed single smooth muscle cells, the time-course response curves induced by the selective alpha1-adrenoceptor agonist, phenylephrine and the selective alpha2-adrenoceptor agonist, UK14304, were similar to those observed with cirazoline and TL99, respectively. 6 These results indicate that: (a) functional alpha1- and alpha2-adre noceptors are present in freshly dispersed single smooth muscle cells from rat tail artery and (b) alpha1- and alpha2-adrenoceptors are coup led to different cellular processes that lead to an increase in intrac ellular Ca2+.