Differential expression of T- and L-type voltage-dependent calcium channels in renal resistance vessels

The distribution of voltage-dependent calcium channels in kidney pre- and p ostglomerular resistance vessels was determined at the molecular and functi onal levels. Reverse transcription-polymerase chain reaction analysis of mi crodissected rat preglomerular vessels and cultured smooth muscle cells sho wed coexpression of mRNAs for T-type subunits (Ca(v)3.1, Ca(v)3.2) and for an L-type subunit (Ca(v)1.2). The same expression pattern was observed in j uxtamedullary efferent arterioles and outer medullary vasa recta. No calciu m channel messages were detected in cortical efferent arterioles. Ca(v)1.2 protein was demonstrated by immunochemical labeling or rat preglomerular va sculature and juxtamedullary efferent arterioles and vasa recta. Cortical e fferent arterioles were not immunopositive. Recordings of intracellular cal cium concentration with digital fluorescence imaging microscopy showed a si gnificant increase of calcium in response to K+ (100 mmol/L) in isolated af ferent arterioles (140 +/- 25%) and in juxtamedullary efferent arterioles ( 118 +/- 21%). These calcium responses were attenuated by the L-type antagon ist calciseptine and by the T-type antagonist mibefradil. Intracellular cal cium increased in response to K+ in cortical efferent arterioles (21 +/- 9% ). Mibefradil and nickel concentration dependently blocked K+-induced contr action of perfused rabbit afferent arterioles. Calciseptine blocked the con traction mediated by K+ (EC50 8 X 10(-14)). S-(-)-Bay K 8644 had no effect on vascular diameter in the afferent arteriole. We conclude that voltage-de pendent L- and T-type calcium channels are expressed and of functional sign ificance in renal cortical preglomerular vessels, in juxtamedullary efferen t arterioles, and in outer medullary vasa recta, but not in cortical effere nt arterioles.