Attenuation of L-Type Ca ²⁺ Channel Expression and Vasomotor Response in the Aorta with Age in Both Wistar-Kyoto and Spontaneously Hypertensive Rats

Abstract

Age-related vascular diseases are induced by vascular dysfunction, which involves changes in the vasomotor response. The voltage-dependent L-type calcium channel (VDCC) protein is involved in the regulation of vessel function (contraction/relaxation action). In the present study, we evaluated age-related vasomotor function and expression of the signal-related target proteins, including VDCC, using thoracic aorta from both 8- and 40-week old Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). In contraction experiments using aortic rings, vasomotor responses of both phenylephrine-induced contraction and acetylcholine-induced relaxation were significantly attenuated with age in SHR, whereas WKY did not lose activity with age. Contraction induced by angiotensin II was impaired only for the 40-week old SHR among all the rat groups tested, although enhanced AT1R/reduced AT2R expression with age was observed for both WKY and SHR. In contrast, a vasomotor responsiveness to Bay K 8644 (a VDCC agonist) at the initial contraction phase was significantly attenuated in both 40-week WKY and SHR with significant reduction of VDCC protein expression. The reduced VDCC expression in 40-week old rats significantly lowered the relaxation activity of VDCC blockers, such as verapamil and Trp-His, but did not affect that of nifedipine. Taken together, we provided the first evidence that aging caused a reduction of VDCC expression in rat aorta, irrespective of the rat strain, along with diminishment of the therapeutic potential of VDCC blockers.