NUCLEOSIDE PHOSPHATASE ACTIVITY IN ATRIAL AND VENTRICULAR MYOCARDIUM OF RAT - A LIGHT AND ELECTRON MICROSCOPIC STUDY

Nucleoside phosphatase activity was studied in glutaraldehyde‐fixed rat myocardium. At pH 7.2, ATPase, nucleoside diphosphatase and thiamine pyrophosphatase activity were demonstrated in the transverse elements of the sarcoplasmic reticulum of ventricular fibers and in the subsarcolemmal cisterns of atrial and ventricular muscle cells. The remainder of the sarcoplasmic reticulum of atrial and ventricular fibers showed reactions only with nucleoside diphosphates. The T tubules and intercalated discs of ventricular muscle reacted strongly with nucleoside monophosphates at pH 7.2; atrial myocardium showed this reaction only in the intercalated discs and in the spaces between closely apposed muscle cells. Thiamine pyrophosphatase and nucleoside diphosphatase were demonstrated in the Golgi apparatus of both atrial and ventricular muscle cells; however, reactive cisterns were more numerous in atrial than in ventricular myocardium. These enzymes were also demonstrated in some of the membranes surrounding the specific cytoplasmic granules of atrial muscle cells. Acid phosphatase activity was also detected in some of these membranes when cytidine monophosphate was used as substrate. Copyright © 1969 Wiley‐Liss, Inc.