Search

The action potential duration (APD) of guinea pig atrial muscle responded qualitatively to metabolic depression and altered glucose concentration as shown previously for papillary muscle. Both preparations lost potassium and gained sodium during 8 h anoxic incubations and these changes were partially prevented by 50 mM glucose. Experiments with potassium indicated that anoxia-induced loss of potassium was not primarily due to an increased efflux but to a decreased influx. Stimulation did not increase potassium efflux from atria but caused some increase in potassium loss. The ATP content of atria and ventricular muscle decreased rapidly during anoxic incubation but was maintained at a significantly higher level in the presence of 50 mM glucose. Since muscle potassium levels following 8 h of anoxic incubation were incompatible with observed resting potentials, the results support the concept of either an electrogenic sodium pump or the intracellular compartmentalization of potassium. In addition, the anoxia-induced reduction of action potential duration does not appear to be associated with an increase in potassium efflux. [ABSTRACT FROM AUTHOR]

The sensitivity of guinea-pig papillary muscle transmembrane electrical activity to alterations in medium glucose concentration increased with time of incubation under anoxic conditions. DNP at a concentration of 10 M produced a decrease in fresh papillary muscle action potential duration comparable to that produced by low medium glucose in muscle after prolonged anoxic incubation. 10 M DNP did not increase the decline in action potential duration of fresh papillary muscle caused by anoxic incubation in medium containing 5 mM glucose. The ATP content of ventricular strips fell to about 30% control during 60 min of anoxia but was maintained at a significantly higher level when the medium contained 50 mM rather than 5 mM glucose. In the presence of 10 M DNP the ATP content of strips fell to 25% control in 10 min and the increased loss was maintained throughout 60 min. During 120 min incubation in medium containing 5 mM glucose and oxygen, the ATP of strips was maintained but the action potential duration declined to 50% control. The results support the proposal that a close association exists between glycolytically produced ATP and transmembrane electrical activity. The effects of DNP on transmembrane electrical activity may be explained by an active depletion of ATP in addition to its uncoupling activity. [ABSTRACT FROM AUTHOR]