Abstract
Desensitization of ligand-gated ion channels shapes synaptic responses and provides critical neuroprotection at central synapses, yet the molecular mechanisms underlying the desensitization process are poorly understood. Using the whole-cell voltage-clamp technique, we investigated desensitization kinetics of recombinant human and guinea pig α-homomeric 5-hydroxytryptamine type 3 (5-HT3A) receptors heterologously expressed in human embryonic kidney 293 cells. Human 5-HT3A receptors desensitize 3.5 times faster than does the homologous receptor from guinea pigs. By constructing various chimeras and through site-directed mutagenesis, we have identified a single serine in the M1 region of the human 5-HT3A receptor sequence (S248) that, when substituted with threonine found in the equivalent guinea pig sequence (T254), conferred guinea pig-like kinetics on the time course of desensitization of the human receptor. Correspondingly, the reverse mutation (guinea pig T254S) resulted in a fast, human-like time constant of desensitization. Thus, the primary structure of the M1 region is an important determinant of desensitization kinetics of recombinant 5-HT3A receptors.
Footnotes
- Received May 11, 2000.
- Accepted December 21, 2000.
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Send reprint requests to: Prof. Dr. Dr. H. Hatt, Dept. of Cell Physiology, Ruhr-University Bochum, Universitätsstrasse 150, 44780 Bochum, Germany. E-mail:hanns.hatt{at}ruhr-uni-bochum.de
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This work was supported by the Deutsche Forschungsgemeinschaft (We2298/1 to C.H.W. and G.G. and KOGNET III to N.L.).
- The American Society for Pharmacology and Experimental Therapeutics
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