We report here the quantitative evaluation of binding density (Bmax) of [3H](+)-PN200-110 in aortic membranes obtained from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. At both 4 and 13 weeks of age, there were no significant differences in Bmax and the dissociation constants (Kd) of [3H](+)-PN200-110 binding between SHR and WKY rat aortas. Irrespective of strain, the Kd increased and the Bmax decreased with age. These results suggest that the number of Ca2+ channels in aortas of SHR and WKY rats are not significantly different, even when hypertension is established in SHR.