Fluid-phase endocytosis by in situ cardiac myocytes of rat atria

• Published in: The American journal of physiology Vol. 265; no. 4 Pt 1; p. C986
• Main Authors: Page, E, Upshaw-Earley, J, Goings, G E, Hanck, D A
• Format: Journal Article
• Language: English
• Published: United States 01.10.1993
• Subjects: Animals; Cell Membrane - ultrastructure; Endocytosis; Extracellular Space - metabolism; Female; Heart - physiology; Heart Atria; Myocardium - cytology; Myocardium - metabolism; Rats; Sucrose - metabolism
• ISSN: 0002-9513
• DOI: 10.1152/ajpcell.1993.265.4.c986

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.