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 pD₂ being 4. 4 and 5.8 respectively. The intracellular Ca²⁺-dependent component of NE-induced aortic strip contraction was also inhibited by the 2 drugs, but the extracellular Ca²⁺-dependent component was barely or not inhibited by Atr before its concentration was raised to 100 μmol/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 μmol/L, but inhibited by Ah 555.7～1666.7 μmol/L, suggesting that Ca²⁺ is somehow involved in the action of Atr on ASMC growth.