Departments of Pharmacology, College of Medicine and Health Sciences, UAE University, Al Ain, United Arab Emirates; Department of Pharmacology and Therapeutics, Faculty of Pharmacy, Kuwait University, Safat, Kuwait. Electronic address: [Email]
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 α7 subunit of the human nicotinic acetylcholine (α7 nACh) receptor were investigated. Ion currents activated by ACh (100 μM) were reversibly inhibited with an IC50 value of 8.6 μM. 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 [125I] α-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 α7-receptor, were reversibly inhibited by 10 min bath application of capsaicin (10 μM). Collectively, results of our investigation indicate that the function of the α7-nACh receptor expressed in Xenopus oocytes and in hippocampal interneurons are inhibited by capsaicin.
