Vascular smooth muscle cells express the α1A subunit of a P-/Q-type voltage-dependent Ca2+ channel, and it is functionally important in renal afferent arterioles

In the present study, we tested whether the alpha (1A) subunit, which encodes a neuronal isoform of voltage-dependent Ca2+ 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 alpha (1A) 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, alpha (1A) subunit protein was demonstrated in rat aorta, brain, aortic smooth muscle cells (A7r5), VSMCs, and mesangial cells. Immunolabeling with an anti-alpha (1A) antibody was positive in acid-macerated, microdissected preglomerular vessels and in A7r5 cells. Patch-clamp experiments on aortic A7r5 cells showed 22+/-4% (n=6) inhibition of inward Ca2+ current by omega -Agatoxin IVA (10(-8) mol/L), which in this concentration is a specific inhibitor of P-type VDCCs. Measurements of intracellular Ca2+ in afferent arterioles with fluorescence-imaging microscopy showed 32+/-9% (n=10) inhibition of the K+-induced rise in Ca2+ in the presence of 10(-8) mol/L omega -Agatoxin IVA. In microperfused rabbit afferent arterioles, omega -Agatoxin IVA inhibited depolarization-mediated contraction with an EC50 of 10(-17) mol/L and complete blockade at 10(-14) mol/L. We conclude that the alpha (1A) subunit is expressed in VSMCs from renal preglomerular resistance vessels and aorta, as well as mesangial cells, and that P-type VDCCs contribute to Ca2+ influx in aortic and renal VSMCs and are involved in depolarization-mediated contraction in renal afferent arterioles.