Voltage-Activated Sodium Current Is Inhibited by Capsaicin in Rat Atrial Myocytes

The effects of capsaicin, the active principle of hot pepper genus Capsicum, were studied on voltage-activated, tetrodotoxin-sensitive Na+ currents in isolated rat atrial cells using the patch clamp technique in the whole-cell configuration. 0.4 and 4 μM of capsaicin produced a significant tonic block on voltage-activated Na+ current (INa) evoked by a depolarizing step to −40 mV from a holding potential of −100 mV (49 ± 7% n = 11, P < 0.05 and 72 ± 13% n = 4, P < 0.05 respectively). We didn't observe any use-dependent block of capsaicin in our experimental conditions. Capsaicin slowed the time decay of inactivation of INa, and increased the time constant of the recovery of inactivation. Capsaicin and tetrodotoxin (TTX) depressed contractility of isolated electrically driven left rat atria, being the depression of maximal velocity of force development (dF/dtmax) with respect to control values of 19 ± 3% at 1 μM of capsaicin and 22 ± 2% at 1 μM of TTX. These results show an inhibitory effect of capsaicin on INa in isolated atrial cells that may modify the electrical and contractile function of the rat heart.