Coexpression of voltage-dependent calcium channels CaV1.2, 2.1a, and 2.1b in vascular myocytes

Voltage-dependent Ca2+ channels Ca(v)1.2 ( L type) and Ca(v)2.1( P/Q type) are expressed in vascular smooth muscle cells (VSMCs) and are important for the contraction of renal resistance vessels. In the present study we examined whether native renal VSMCs coexpress L-, P-, and Q-type Ca2+ currents. The expression of both Ca(v)2.1a ( P- type) and Ca(v)2.1b (Q-type) mRNA was demonstrated by RT-PCR in renal preglomerular vessels from rats and mice. Immunolabeling was performed on A7r5 cells, renal cryosections, and freshly isolated renal VSMCs with anti-Ca(v)1.2 and anti-Ca(v)2.1 antibodies. Conventional and confocal microscopy revealed expression of both channels in all of the smooth muscle cells. Whole-cell patch clamp on single preglomerular VSMCs from mice showed L-, P-, and Q-type currents. Blockade of the L- type currents by calciseptine ( 20 nmol/L) inhibited 35.6 +/- 3.9% of the voltage-dependent Ca2+ current, and blocking P- type currents ( omega-agatoxin IVA 10 nmol/L) led to 20.2 +/- 3.0% inhibition, whereas 300 nmol/L of omega agatoxin IVA ( blocking P/Q-type) inhibited 45.0 +/- 7.3%. In rat aortic smooth muscle cells ( A7r5), blockade of L- type channels resulted in 28.5 +/- 6.1% inhibition, simultaneous blockade of L- type and P- type channels inhibited 58.0 +/- 11.8%, and simultaneous inhibition of L-, P-, and Q-type channels led to blockade ( 88.7 +/- 5.6%) of the Ca2+ current. We conclude that aortic and renal preglomerular smooth muscle cells express L-, P-, and Q-type voltage-dependent Ca2+ channels in the rat and mouse.