Capsaicin inhibits the function of α7-nicotinic acetylcholine receptors expressed in Xenopus oocytes and rat hippocampal neurons

Capsaicin is a naturally occurring alkaloid derived from Chili peppers fruits. Using the two-electrode voltage-clamp technique in Xenopus oocyte expression system, actions of capsaicin on the functional properties of alpha(7) subunit of the human nicotinic acetylcholine (alpha(7) nACh) receptor were investigated. Ion currents activated by ACh (100 mu M) were reversibly inhibited with an IC50 value of 8.6 mu M. Inhibitory actions of capsaicin was independent of membrane potential. Furthermore, Ca2+-dependent Cl- channels expressed endogenously in oocytes were not involved in inhibitory actions of capsaicin. In addition, increasing the ACh concentrations could not reverse the inhibitory effects of capsaicin. Importantly, specific binding of [I-125] alpha-bungarotoxin remained unaltered by capsaicin suggesting that its effect is noncompetitive. Whole cell patch-clamp technique was performed in CA1 stratum radiatum interneurons of rat hippocampal slices. Ion currents induced by choline, a selective-agonist of alpha(7)-receptor, were reversibly inhibited by 10 min bath application of capsaicin (10 mu M). Collectively, results of our investigation indicate that the function of the alpha 7-nACh receptor expressed in Xenopus oocytes and in hippocampal interneurons are inhibited by capsaicin.