Fluid-phase endocytosis by in situ cardiac myocytes of rat atria.
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.
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Department of Medicine, University of Chicago, Illinois 60637.
Upshaw-Earley
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Goings
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GE
Hanck
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DA
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
D013395:Sucrose