EFFECT OF CAPSAICIN ON MEMBRANE CURRENTS IN CULTURED VASCULAR SMOOTH-MUSCLE CELLS OF RAT AORTA

The application of capsaicin (1 mu M) produced a minor relaxant effect in endothelium-denuded rat aortae. However, capsaicin caused a greate r relaxation of blood vessels precontracted with high K+ or phenylephr ine. The effects of capsaicin on the ionic currents were also examined in A7r5 vascular smooth muscle cells. The tight-seal whole-cell volta ge clamp technique was used. Capsaicin inhibited the Ba2+ inward curre nt (I-Ba) through the voltage-dependent L-type Ca2+ channel in a conce ntration-dependent fashion, whereas calcitonin gene-related peptide an d phenylephrine produced a minor increase in I-Ba. Capsaicin did not a lter the overall shape of current-voltage relationship of I-Ba. Howeve r, capsaicin (3 mu M) Shifted the quasi-steady-state inactivation curv e of I-Ba to more negative membrane potential by about 5 mV. These eff ects of capsaicin on I-Ba were reversible. In addition, capsaicin had inhibitory effects on voltage dependent K+ currents. These results sug gest that inhibition of the voltage-dependent L-type Ca2+ channel is i nvolved in the capsaicin-induced relaxation of the vascular smooth mus cle, whereas capsaicin-induced inhibition of voltage-dependent K+ chan nels might produce an increase in cell excitability.