Enzyme histochemical studies on the Purkinje fibers of the atrioventricular system of the bovine and porcine hearts.

In this communication the results of applying various histochemical semipermeable membrane techniques to the localization of several enzymes in bovine and porcine heart are presented. The Purkinje fibers of the atrioventricular conducting system of the bovine heart differ from the myocardium proper in containing a greater activity of the glycolytic and gluconeogenetic enzymes--lactate dehydrogenase, glyceraldehyde-phosphate dehydrogenase, hexokinase, glucosephosphate isomerase and phosphoglucomutase, and less activity of the aerobic enzymes--NADH: nitroBT oxidoreductase and isocitrate dehydrogenase (NADP+). The metabolic reactions obtained with Purkinje fibers of the porcine heart are less pronounced. These histochemical findings are in accordance with the impression that Purkinje fibers, compared with the common myocardial fibers, have a higher rate of anaerobic metabolism and a lower rate of aerobic metabolism. The activity of the NADPH regenerating enzymes glucose-6-phosphate dehydrogenase and phosphogluconate dehydrogenase (decarboxylating), and the activity of acid hydrolases such as non-specific esterase and acid phosphatase is higher in the Purkinje fibers of both the bovine and porcine heart.