title: Functional acetylcholine receptor--electroplax membrane microsacs (vesicles): purification and characterization.
abstract: Kinetic analysis of the flux of sodium ions in a heterogeneous population of acetylcholine receptor-rich microsacs (vesicles) formed by membrane fragments of electroplax indicated that functional microsacs, which on average comprise only 15% of the preparation, can be filled with 190 mM sodium chloride while nonfunctional microsacs are filled by 190 mM cesium chloride. The functional microsacs have then been successfully separated from nonfunctional microsacs on the basis of their density differences with a continuous sucrose-190 mM cesium chloride density gradient. In the presence of acetylcholine analogs all the internal sodium ions in these microsacs rapidly exchange with external ions. The efflux of sodium ions follows a single exponential decay. The isolation of functional microsacs opens up at least two new avenues of investigation of the molecular mechanism of receptor-mediated processes. The first deals with the efficiency of the process, and the second with the characterization of membrane components important in this process. The conclusions reached so far are: (i) The efficiency of the receptor-mediated process that allows inorganic ions to equilibrate across the membranes of the microsacs can adequately account for electrophysiological results obtained with muscle and nerve cells. (ii) In the receptor-rich heterogeneous population of microsacs the concentration of receptor sites in functional and nonfunctional microsacs is about the same and is therefore not the only factor determining functionality. Significant differences between functional and nonfunctional microsacs have been found so far in the concentrations of acetylcholinesterase and Na+-K+ ATPase.
mesh_terms: D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D004524:Eels; D004557:Electric Organ / Q000378:metabolism*; D007700:Kinetics; D011950:Receptors, Cholinergic / Q000302:isolation & purification / Q000378:metabolism; D012964:Sodium / Q000378:metabolism
chemical_list: D011950:Receptors, Cholinergic; D012964:Sodium; D000109:Acetylcholine
references.citation: Arch Biochem Biophys. 1961 Dec;95:416-23
references.pmid: 13871109
references.citation: Biochem Pharmacol. 1961 Jul;7:88-95
references.pmid: 13726518
references.citation: Harvey Lect. 1953-1954;49:57-99
references.pmid: 13232543
references.citation: J Biol Chem. 1951 Nov;193(1):265-75
references.pmid: 14907713
references.citation: J Physiol. 1951 Nov 28;115(3):320-70
references.pmid: 14898516
references.citation: Anal Biochem. 1976 Oct;75(2):454-63
references.pmid: 984406
references.citation: J Physiol. 1972 Aug;224(3):665-99
references.pmid: 5071933
references.citation: J Physiol. 1973 Dec;235(3):655-91
references.pmid: 4543940
references.citation: Annu Rev Pharmacol. 1972;12:265-86
references.pmid: 4339019
references.citation: Cold Spring Harb Symp Quant Biol. 1976;40:211-30
references.pmid: 181196
references.citation: Q Rev Biophys. 1974 Jul;7(3):283-399
references.pmid: 4449983
references.citation: Biochem Biophys Res Commun. 1974 Oct 8;60(3):1072-80
references.pmid: 4429562
references.citation: Arch Biochem Biophys. 1973 Nov;159(1):362-73
references.pmid: 4806354
references.citation: Biochem Biophys Res Commun. 1973 Sep 18;54(2):677-84
references.pmid: 4756794
references.citation: Cold Spring Harb Symp Quant Biol. 1976;40:203-10
references.pmid: 820505
references.citation: Cold Spring Harb Symp Quant Biol. 1976;40:231-5
references.pmid: 1065526
references.citation: Cold Spring Harb Symp Quant Biol. 1976;40:193-202
references.pmid: 1065525
references.citation: Ann N Y Acad Sci. 1975 Dec 30;264:183-202
references.pmid: 769639
references.citation: Proc Natl Acad Sci U S A. 1975 Nov;72(11):4371-5
references.pmid: 1060114
references.citation: Biochem Biophys Res Commun. 1976 Apr 5;69(3):830-7
references.pmid: 1267819
references.citation: Biochem Biophys Res Commun. 1976 Jun 7;70(3):1020-7
references.pmid: 938522
references.citation: Biochem Biophys Res Commun. 1976 Jan 12;68(1):56-63
references.pmid: 942851
references.citation: Biochem Biophys Res Commun. 1975 Jan 2;64(3):1018-27
references.pmid: 1147955
references.citation: J Biol Chem. 1975 Mar 10;250(5):1776-81
references.pmid: 1167546