Functional properties of homomeric, human α7-nicotinic acetylcholine receptors heterologously expressed in the SH-EP1 human epithelial cell line

alpha7-Nicotinic acetylcholine receptors (alpha7-nAChRs) are broadly distributed in the central nervous system, where they play important roles in chemical and electrical signaling, and perhaps in neurite outgrowth, synaptic plasticity, and neuronal death/survival. To help elucidate their normal and pathophysiological roles, we have heterologously expressed human alpha7-nAChR in transfected SH-EP1 human epithelial cells. Reverse transcription-polymerase chain reaction and mRNA fluorescence in situ hybridization analyses demonstrate expression of human alpha7 subunits as messenger RNA. Patch-clamp recordings exploiting a novel strategy to prevent functional rundown of whole-cell peak current responses to repeated acute challenges with nicotinic agonists show successful expression of functional alpha7-nAChR that mediate inward currents characterized by rapid phases of activation and inactivation. Concentration-response curves show that nicotine, acetylcholine, and choline are efficacious agonists at human alpha7-nAChRs. Current-voltage relationships show inward rectification for agonist-induced currents. Human alpha7-nAChRs exhibit some sensitivity to alpha7-nAChR antagonists alpha-bungarotoxin (Bgt) or methyllycaconitine (MLA) when applied coincidentally with agonist, but much higher affinity block occurs when cells and alpha7-nAChRs are pre-exposed to antagonists for 2 min before challenge with agonist. Both Bgt and MLA are competitive inhibitors of alpha7-nAChR function. Whole-cell current peak amplitudes and halftimes for inactivation of alpha7-nAChR functional responses to nicotine are dramatically reduced in the absence of extracellular Ca2+, suggestive of high Ca2+ permeability of the alpha7-nAChR channel. Thus, heterologously expressed human alpha7-nAChR in mammalian cells have properties of native alpha7-nAChR or of alpha7-nAChR heterologously expressed in other systems and serve as excellent models for studies of molecular bases of alpha7-nAChR function.