[Effects of atropine on contraction of rabbit aortic smooth muscle and cell proliferation]

The calcium antagonistic actions of atropine (Atr) and verapamil (Ver) were studied on the contraction of rabbit thoracic aorta strips induced by CaCl2 and KCl. Both Atr and Ver were found to depress the contraction as demonstrated by the shift-to-right of the dose-effect relationship curves and the decrease of maximal responses, with the value of pD'2 being 4.4 and 5.8 respectively. The intracellular Ca(2+)-dependent component of NE-induced aortic strip contraction was also inhibited by the 2 drugs, but the extracellular Ca(2+)-dependent component was barely or not inhibited by Atr before its concentration was raised to 100 mumol/L. These results indicate that the depressive effect of Atr on aortic contraction is mainly exerted by acting on the PDC (potential-dependent channel). The action of Atr on proliferation of cells was also studied in rabbit aortic smooth muscle cell (ASMC) culture. The growth was inhibited by Atr when Ca2+ was present in the medium. When Ca2+ was absent, however, the growth was stimulated by Atr 20.6-185.2 mumol/L, but inhibited by Atr 555.7-1666.7 mumol/L, suggesting that Ca2+ is somehow involved in the action of Atr on ASMC growth.