| Abstract
| - SUMMARY. The action potential duration (APD) was measured using an Ag-AgCl electrode, in open chest anaesthetised dogs (n = 8) and puppies, 4 to 6 months old (n=8), with complete atrio-ventricular dissociation and β-adrenergic blockade. They were paced in the control period at a frequency of 120 beats·min−1. Both adults and puppies showed maximum action potential duration at a test pulse interval of over 700 ms. Below this the adult dogs showed a progressive shortening of the action potential duration (mean APD 81.5% at 200 ms). In contrast, the puppies showed much less shortening (91% at 200 ms; p<0.001). Measurements of Na+, K+-ATPase activity by the Rb uptake method gave values of 13.4± 1.3 (puppies, n = 4) and 6.1 ± 1.1 (adults, n = 6). These results may be consistent with the idea of a greater influx and efflux of sodium in the myocardial cells of the puppy compared with the adult dog.
|
