Effect of capsaicin on membrane currents in cultured vascular smooth muscle cells of rat aorta

Abstract

The application of capsaicin (1 μM) produced a minor relaxant effect in endothelium-denuded rat aortae. However, capsaicin caused a greater relaxation of blood vessels precontracted with high K⁺ or phenylephrine. The effects of capsaicin on the ionic currents were also examined in A7r5 vascular smooth muscle cells. The tight-seal whole-cell voltage clamp technique was used. Capsaicin inhibited the Ba²⁺ inward current (I_Ba) through the voltage-dependent L-type Ca²⁺ channel in a concentration-dependent fashion, whereas calcitonin gene-related peptide and phenylephrine produced a minor increase in I_Ba. Capsaicin did not alter the overall shape of current-voltage relationship of I_Ba. However, capsaicin (3 μM) shifted the quasi-steady-state inactivation curve of I_Ba to more negative membrane potential by about 5 mV. These effects of capsaicin on I_Ba were reversible. In addition, capsaicin had inhibitory effects on voltage dependent K⁺ currents. These results suggest that inhibition of the voltage-dependent L-type Ca²⁺ channel is involved in the capsaicin-induced relaxation of the vascular smooth muscle, whereas capsaicin-induced inhibition of voltage-dependent K⁺ channels might produced an increase in cell excitability.