Acetylcholine and electrolyte metabolism in the various chambers of the frog and turtle heart

Evidence has accumulated suggesting acetylcholine may he involved in initiation of the heart heat. Acetylcholine and electrolyte metabolism in the various chambers of the heart have been studied. The area of highest intrinsic rhythm (sinus) contained greater amounts of acetylcholine equivalents, true cholinesterase, choline acetylase and sodium; all of these decreasing in amount in areas of lower intrinsie rhythm. It is concluded that intrinsic rhythm may he directly correlated with overall acetylcholine metabolism and sodium content and inversely related to overall energy metabolism and potassium concentration.

Effect of temperature on the heart rate, electrocardiogram and certain myocardial oxidations of the rat

Deep hypothermia in the rat was studied with respect to the sequential changes in body temperature, heart rate, and electrocardiogram. In vitro assays of myocardial metabolic activity were made at temperatures ranging from 5 to 35 C. These assays strongly suggested that the in vivo cardiac dysfunctions observed at low temperatures were attributable to shifts in temperature kinetics of enzyme systems at 20 to 21 C.

High energy phosphates during hibernation and arousal in the ground squirrel

Biochemical levels of inorganic phosphate, adenosine triphosphate, phosphocreatine and glycogen were determined on cardiac muscle, skeletal muscle and liver samples from hibernated 13-striped ground squirrels and those allowed to awaken for intervals of 7.5, 15 and 30 minutes. Cardiac muscle glycogen increases during hibernation apparently at the expense of skeletal muscle and liver glycogen. Glycolysis occurs in these tissues during early arousal, followed later by glycogenesis. Adenosine triphosphate is maintained in both cardiac and skeletal muscle during hibernation and is used as an energy source during arousal. It appears that glycolysis is important in resynthesizing phosphocreatine. From this study of periods of relatively low and high metabolic demands we conclude that phosphocreatine is a ‘transport’ form of high-energy phosphate forming adenosine triphosphate from the phosphate pool when and where needed in the cycle of intermediary metabolism.

Effect of ouabain on potassium exchange in heart muscle mitochondria

Potassium in the working frog ventricle exists in two physiological compartments and the more slowly exchanging compartment is influenced by the amount of work performed, ventricular failure and ouabain. In the present study, the exchange of potassium in mitochondria is investigated both in the control state and after exposure to ouabain, in order to determine whether mitochondria potassium represents the slowly exchanging compartment. Mitochondria potassium represents only 15% of the total ventricular potassium, while the slowly exchanging phase contains about 50%. Ouabain perfusion is associated with inhibition of entrance of potassium into the slowly exchanging ventricular phase, but no isolated specific effect on the mitochondria potassium is found. Alterations in mitochondria potassium directly reflect changes within the total ventricle. A fraction of mitochondria potassium is found to be inexchangeable under the conditions of the experiment. The results indicate that mitochondria potassium does not represent the major part of the slowly exchanging compartment.