Vascular smooth muscle cells express the alpha(1A) 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 encod es a neuronal isoform of voltage-dependent Ca2+ channels (VDCCs) (P-/Q-type ), was present and functional in vascular smooth muscle and renal resistanc e vessels. By reverse transcription-polymerase chain reaction and Southern blotting analysis, mRNA encoding the alpha (1A) subunit was detected in mic rodissected rat preglomerular vessels and vasa recta, in cultures of rat pr eglomerular vascular smooth muscle cells (VSMCs), and in cultured rat mesan gial cells. With immunoblots, alpha (1A) subunit protein was demonstrated i n rat aorta, brain, aortic smooth muscle cells (A7r5), VSMCs, and mesangial cells. Immunolabeling with an anti-alpha (1A) antibody was positive in aci d-macerated, microdissected preglomerular vessels and in A7r5 cells. Patch- clamp experiments on aortic A7r5 cells showed 22+/-4% (n=6) inhibition of i nward Ca2+ current by omega -Agatoxin IVA (10(-8) mol/L), which in this con centration is a specific inhibitor of P-type VDCCs. Measurements of intrace llular Ca2+ in afferent arterioles with fluorescence-imaging microscopy sho wed 32+/-9% (n=10) inhibition of the K+-induced rise in Ca2+ in the presenc e of 10(-8) mol/L omega -Agatoxin IVA. In microperfused rabbit afferent art erioles, omega -Agatoxin IVA inhibited depolarization-mediated contraction with an EC50 of 10(-17) mol/L and complete blockade at 10(-14) mol/L. We co nclude that the alpha (1A) subunit is expressed in VSMCs from renal preglom erular 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 inv olved in depolarization-mediated contraction in renal afferent arterioles.