Kinetics of desensitization and recovery from desensitization for human alpha4beta2-nicotinic acetylcholine receptors stably expressed in SH-EP1 cells.
OBJECTIVE
Studies were conducted to define the kinetics of the onset of and recovery from desensitization for human alpha4beta2-nicotinic acetylcholine receptors (nAChR) heterologously expressed in the SH-EP1 human epithelial cell line.


METHODS
Whole-cell patch clamp recordings were performed to evaluate alpha4beta2-nAChR currents.


RESULTS
Application of 0.1 micromol/L nicotine or 1 mmol/L acetylcholine (ACh) for 1 s or longer induced two phases, with time constants of approximately 70 and approximately 700 ms, for the onset of alpha4beta2-nAChR desensitization. For a given duration of agonist exposure, recovery from desensitization induced by nicotine was slower than recovery from ACh-induced desensitization. Comparisons with published reports indicate that time constants for the recovery of alpha4beta2-nAChRs from desensitization are smaller than those for the recovery of human muscle-type nAChRs(1) from desensitization produced by the same concentrations and durations of exposure to an agonist. Moreover, the extent of human alpha4beta2-nAChR desensitization and rate of recovery are the same, regardless of whether they are measured using whole-cell recording or based on published findings(2) using isotopic ion flux assays; this equality demonstrates the equivalent legitimacy of these techniques in the evaluation of nAChR desensitization. Perhaps most significantly, recovery from desensitization also was best fit to a biphasic process. Regardless of whether it was fit to single or double exponentials, however, half-times for recovery from desensitization grew progressively longer with an increased duration of agonist exposure during the desensitizing pulse.


CONCLUSIONS
These findings indicate the existence of alpha4beta2-nAChRs in many distinctive states of desensitization, as well as the induction of progressively deeper states of desensitization with the increased duration of agonist exposure.
Yu
Kewei D
KD
Division of Neurology, Barrow Neurological Institute, Phoenix, AZ 85013, USA.
Liu
Qiang
Q
Wu
Jie
J
Lukas
Ronald J
RJ
D000109:Acetylcholine / Q000008:administration & dosage / Q000494:pharmacology*; D002460:Cell Line; D018678:Cholinergic Agents / Q000008:administration & dosage / Q000494:pharmacology; D004594:Electrophysiology / Q000379:methods; D004847:Epithelial Cells; D006801:Humans; D009538:Nicotine / Q000008:administration & dosage / Q000494:pharmacology*; D018722:Nicotinic Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors
D018678:Cholinergic Agents; D018722:Nicotinic Agonists; D011978:Receptors, Nicotinic; C403531:nicotinic receptor alpha4beta2; D009538:Nicotine; D000109:Acetylcholine