Vascular Smooth Muscle Cells Express the a1A Subunit of a P-/Q-Type Voltage-Dependent CaChannel, and It Is Functionally Important in Renal Afferent Arterioles

In the present study, we tested whether the a1A subunit, which encodes a neuronal isoform of voltage-dependent Ca channels (VDCCs) (P-/Q-type), was present and functional in vascular smooth muscle and renal resistance vessels. By reverse transcription–polymerase chain reaction and Southern blotting analysis, mRNA encoding the a1A subunit was detected in microdissected rat preglomerular vessels and vasa recta, in cultures of rat preglomerular vascular smooth muscle cells (VSMCs), and in cultured rat mesangial cells. With immunoblots, a1A subunit protein was demonstrated in rat aorta, brain, aortic smooth muscle cells (A7r5), VSMCs, and mesangial cells. Immunolabeling with an anti-a1A antibody was positive in acid-macerated, microdissected preglomerular vessels and in A7r5 cells. Patch-clamp experiments on aortic A7r5 cells showed 2264% (n56) inhibition of inward Ca current by v-Agatoxin IVA (10 mol/L), which in this concentration is a specific inhibitor of P-type VDCCs. Measurements of intracellular Ca in afferent arterioles with fluorescence-imaging microscopy showed 3269% (n510) inhibition of the K-induced rise in Ca in the presence of 10 mol/L v-Agatoxin IVA. In microperfused rabbit afferent arterioles, v-Agatoxin IVA inhibited depolarization-mediated contraction with an EC50 of 10 –17 mol/L and complete blockade at 10 mol/L. We conclude that the a1A subunit is expressed in VSMCs from renal preglomerular resistance vessels and aorta, as well as mesangial cells, and that P-type VDCCs contribute to Ca influx in aortic and renal VSMCs and are involved in depolarization-mediated contraction in renal afferent arterioles. (Circ Res. 2000;87:896-902.)