Cocaine potently blocks neuronal α₃β₄ nicotinic acetylcholine receptors in SH-SY5Y cells

Cocaine is one of the most abused illicit drugs worldwide. It is well known that the dopamine (DA) transporter is its major target; but cocaine also acts on other targets including nicotinic acetylcholine receptors (nAChRs). In this study, we investigated the effects of cocaine on a special subtype of neuronal nAChR, α₃β₄-nAChR expressed in native SH-SY5Y cells. α₃β₄-nAChR-mediated currents were recorded using whole-cell recordings. Drugs were applied using a computer-controlled U-tube drug perfusion system. We showed that bath application of nicotine induced inward currents in a concentration-dependent manner with an EC₅₀ value of 20 µM. Pre-treatment with cocaine concentration-dependently inhibited nicotine-induced current with an IC₅₀ of 1.5 μM. Kinetic analysis showed that cocaine accelerated α₃β₄-nAChR desensitization, which caused a reduction of the amplitude of nicotine-induced currents. Co-application of nicotine and cocaine (1.5 μM) depressed the maximum response on the nicotine concentration-response curve without changing the EC₅₀ value, suggesting a non-competitive mechanism. The cocaine-induced inhibition of nicotine response exhibited both voltage- and use-dependence, suggesting an open-channel blocking mechanism. Furthermore, intracellular application of GDP-βS (via recording electrode) did not affect cocaine-induced inhibition, suggesting that cocaine did not alter receptor internalization. Moreover, intracellular application of cocaine (30 µM) failed to alter the nicotine response. Finally, cocaine (1.5 μM) was unable to inhibit the nicotine-induced inward current in heterologous expressed α₆/α₃β₂β₃-nAChRs and α₄β₂-nAChRs expressed in human SH-EP1 cells. Collectively, our results suggest that cocaine is a potent blocker for native α₃β₄-nAChRs expressed in SH-SY5Y cells.