Activation and Ca21 Permeation of Stably Transfected a3/b4 Neuronal Nicotinic Acetylcholine

The a3/b4 rat neuronal nicotinic acetylcholine receptor, stably transfected in human embryonic kidney cells, was examined using the whole-cell-clamp technique and 2-dimensional con-focal imaging. Application of agonists (nicotine, cytisine, epi-batidine) activated a large (100–200 pA/pF) inwardly rectifying monovalent current, with little current at voltages between 0 and 140 mV. Rapid application of nicotine and cytisine indi-cated EC50 values of>22 and>64 mM, respectively, and suggested second order binding kinetics (Hill coefficient;2). The time constant of desensitization (decay) of nicotine-acti-vated current was concentration-dependent (typically;10 s at 30 mM versus;1.0 s at 100–1000 mM), but not voltage-depen-dent and was significantly smaller than the;200 s reported for the a3/b4 receptor expressed in Xenopus oocytes. Nicotine