标题：Comparison of acetylcholine receptor-controlled cation flux in membrane vesicles from Torpedo californica and Electrophorus electricus: Chemical kinetic measurements in the millisecond region
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1982
卷号：79
期号：4
页码：963-967
DOI：10.1073/pnas.79.4.963
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：In earlier studies with the acetylcholine receptor (AcChoR) of Electrophorus electricus the rate and equilibrium constants for a model that relates the ligand binding to ion translocation were determined, and the dependence of these constants on the concentrations of carbamoylcholine and acetylcholine, over a 200- and 5000-fold range, respectively, could be predicted. AcChoR-controlled cation flux has now been measured in Torpedo californica vesicles by using a pulsed-quench-flow technique with a 2-msec time resolution. Torpedo vesicles on a weight basis may contain several hundred times more receptor sites than do E. electricus vesicles. Techniques have been developed to (i) correct for the kinetic heterogeneity of the vesicle population; (ii) use the inactivation of the receptor by its natural ligand to reduce influx rates at high ligand concentrations to a measurable level (this permitted JA, the influx rate coefficient before the onset of inactivation, to be measured); and (iii) determine the rate coefficients of two processes that lead to successive inactivations (desensitization) of the receptor and occur in different time regions. An extension of a model proposed for the E. electricus receptor accommodates the ion translocation in T. californica vesicles. The features in common are: (i) A rapid initial flux rate [JA(max) for T. californica is 310 sec-1; for E. electricus it is 7.5 sec-1]. These differences in flux rates are consistent with a difference in AcChoR density. (ii) A rapid inactivation process [(max) for T. californica is 2 sec-1; for E. electricus it is 7 sec-1]. (iii) A slow AcChoR-controlled flux that continues after the rapid inactivation [JI(max) for T. californica is 1.3 sec-1; for E. electricus it is 0.015 sec-1]. The main difference between the flux in the two types of vesicle is the existence of a second, slower, inactivation process in T. californica with a rate coefficient, {beta
