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L-Type Ca²⁺ Channel Regulation by Pituitary Adenylate Cyclase-Activating Polypeptide in Vascular Myocytes from Spontaneously Hypertensive Rats¹

Departments of Physiology and Medicine (C.L.C.), University of Alberta, Edmonton, Alberta, Canada T6G 2H7

Address all correspondence and requests for reprints to: Dr. E. Karpinski, 7–35 Medical Sciences Building, University of Alberta, Edmonton, Alberta, Canada T6G 2H7. E-mail: ed.karpinski{at}ualberta.ca

Pituitary adenylate cyclase-activating polypeptide (PACAP), a vasoactive peptide, modulates the L-type Ca²⁺ channel current (L channel current) in vascular smooth muscle cells (VSMC) through activation and integration of two intracellular pathways, protein kinase A and protein kinase C (PKC). In the present study we compared the effects of PACAP on the L channel current in VSMC from the spontaneously hypertensive rats (SHR) and normotensive controls, Wistar Kyoto rats (WKY). We found that compared with WKY, VSMC from SHR had a higher L channel current density. Stimulation by PACAP (10 nM) caused an increase in the amplitude of the whole cell current and prolonged open time in VSMC from SHR and WKY, with the increase greater in SHR. These effects of PACAP on the L channel current was mimicked by an activator of PKC. In contrast, PACAP caused a smaller increase in cAMP accumulation in VSMC from SHR than WKY, and there was no difference in the inhibitory effect of 8-bromo-cAMP on the L channel current from both type of cells. The greater increase in amplitude of the L channel current by PACAP in VSMC from SHR persisted in the presence of adenosine cyclic 3',5'-monophosphothioate, Rp-isomer, a cAMP antagonist, but not calphostin C, a PKC inhibitor. Taken together, our results show an increase in L channel current density and an enhanced PACAP effect on the L channel current in VSMC from SHR compared with WKY. This difference in PACAP response appears to be predominately secondary to an increased PKC sensitivity.

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