ULTRASTRUCTURAL ALTERATIONS PRODUCED IN MAMMALIAN MYOCARDIUM BY VARIATION IN PERFUSATE IONIC COMPOSITION

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Abstract
The changes described are produced in the subcellular morphology of mammalian myocardium when perfusate Na, Ca, and Cl concentrations are varied. Using a recently developed perfusion technique, functioning dog papillary muscles were perfused with isotonic solutions of varying ionic compositions. Examination of the tissue in the electron microscope revealed that control muscles showed satisfactory preservation of ultrastructure, demonstrating that the protocol itself did not create significant morphological artefact. Low sodium chloride perfusion produced dilatation of both transverse tubules and longitudinal sarcoplasmic reticulum elements. Low Na or high Ca concentrations produced dilation of tubular elements of the longitudinal sarcoplasmic reticulum while leaving transeverse tubules intact. High Ca perfusion produced mitochondrial swelling and vacuolization. Mitochondrial precipitate, both crystalline and amorphous in form, was observed and presumed to be calcium phosphate, either alone or mixed with calcium carbonate. The possibility that the morphological changes observed might indicate subcellular loci of specific ion permeability is discussed. A correlation of the known kinetic behavior of Na and Ca ions in mammalian myocardium with the ultrastructural alterations produced is suggested.