title: Fluid-phase endocytosis by in situ cardiac myocytes of rat atria.
abstract: Fluid-phase endocytosis (FPE) associated with recycling of fused plasmalemma-secretory granules or membranes and/or membrane receptors by in situ cardiac myocytes was studied at 37 degrees C in vitro noncontracting adult rat atrial preparations. Measurements included 1) the volume (VS*) of the compartment consisting of presumptive endocytotic vesicles and the endosomes or lysosomes transiently in continuity with them (S*), which internalizes [14C]-sucrose but is inaccessible to simultaneously measured [methoxy-3H]inulin, 2) the kinetics of [14C]sucrose efflux from S*, and 3) morphometry to quantify interstitial space and non-heart muscle cells. Vs* (0.39 +/- 0.04 ml/g dry atrium for unstretched atria at 37 degrees C) was 1) variable over a 3.7-fold range under various experimental conditions, 2) significantly increased by neomycin or by lowering the temperature to 18 degrees C, and 3) significantly decreased by alpha 1-adrenergic stimulation. Analysis of sucrose efflux kinetics confirmed the presence of an intramyocytic sucrose-containing compartment. A smaller inulin-inaccessible sucrose space (S*) was also present in right ventricle. Thus, during FPE, vesicles and endosomes initially containing high (extracellular) Ca2+ and Cl- concentrations continually enter, circulate within, and undergo exocytosis from myocardial cells.
authors.affiliation: Department of Medicine, University of Chicago, Illinois 60637.
authors.forename: E
authors.initials: E
authors.lastname: Page
authors.forename: J
authors.initials: J
authors.lastname: Upshaw-Earley
authors.forename: G E
authors.initials: GE
authors.lastname: Goings
authors.forename: D A
authors.initials: DA
authors.lastname: Hanck
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000648:ultrastructure; D004705:Endocytosis; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D006321:Heart / Q000502:physiology*; D006325:Heart Atria; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D051381:Rats; D013395:Sucrose / Q000378:metabolism
chemical_list: D013395:Sucrose