In vitro experiments were performed using small volume chambers (50ml) to evaluate the contractile activity of the canine basilar and femoral arteries. The contractile activity of the basilar arteries were very different from the femoral arteries. Calcium-release contractions of the basilar arteries which were produced in calcium-free buffer solution were lower than the femoral arteries. Potassium (60 mM) ions induced substantial contractions to the femoral arteries even in calcium-free solution, but none to the basilar arteries.
On the other hand, postglandin F_2α and serotonin acted additively on the basilar arteries in both of the calcium release and the maximal contractions, but not on the femoral arteries.
The basilar arteries needed the minimal concentration of 10^-5 M calcium ions in buffer solution for contractions induced by serotonin. And also, if pretreated with high concentration of calcium ions (10mM), calcium release contractions of the basilar arteries were significantly increased. Concerning contractions of the basilar arteries, it seems likely that influx of calcium ions through the cell membrane of vascular smooth muscle depends predominantly on the receptor-operated channels and in the femoral arteries the potential-sensitive channels play main role on influx of calcium ions for their contractions. Also extracellular concentration of calcium ions which is necessary to induce contractions of the basilar arteries is about 100 folds of the intracellular calcium ions.