L-Type Calcium Channels in Vascular Smooth Muscle Cells from Spontaneously Hypertensive Rats: Effects of Calcium Agonist and Antagonist

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Studies using the whole-cell voltage-clamp technique have demonstrated that L-type Ca²⁺ channel activity is increased in vascular smooth. muscle cells from spontaneously hypertensive rats (SHR). We recorded L-type Ca²⁺ channel currents in cultured mesenteric artery smooth muscle cells from SHR and Wistar Kyoto (WKY) rats by using the cell-attached patch-clamp technique. Depolarizing voltage steps from a holding potential of -40mV elicited voltage-dependent inward Ba²⁺ currents. There was no difference in the L-type Ca²⁺ channel I-V curve or in the open probability between SHR and WKY. The inward currents were inhibited by the Ca²⁺ antagonists nifedipine and verapamil, but were enhanced by the Ca²⁺ agonist Bay K 8644 in a concentration-dependent manner. The Bay K 8644-induced increase and the nifedipine-induced inhibition of the inward currents were enhanced in SHR, whereas there was no difference in the verapamil-induced inhibition of the currents between the two strains of rats. These results suggest that the enhanced L-type Ca²⁺ channel activity observed in vascular smooth muscle cells from SHR is not due to altered function of a single L-type Ca²⁺ channel. It appears that the sensitivity of dihydropyridine receptors in the channels is enhan ced in SHR. (Hypertens Res 1998; 21: 33-37)