Changes in Ca²⁺ cycling proteins underlie cardiac action potential prolongation in a pressure-overloaded guinea pig model with cardiac hypertrophy and failure

Ventricular arrhythmias are common in both cardiac hypertrophy and failure; cardiac failure in particular is associated with a significant increase in the risk of sudden cardiac death. We studied the electrophysiologic changes in a guinea pig model with aortic banding resulting in cardiac hypertrophy at 4 weeks and progressing to cardiac failure at 8 weeks using whole-cell patch-clamp and biochemical techniques. Action potential durations (APDs) were significantly prolonged in banded animals at 4 and 8 weeks compared with age-matched sham-operated animals. APDs at 50% and 90% repolarization (APD₅₀ and APD₉₀ in ms) were the following: 4 week, banded, 208±51 and 248±49 (n= 15); 4 week, sham, 189±68 and 2132±69 (n= 16); 8 week, banded, 197±40 and 226±40 (n=21); and 8 week, sham, 156±42 and 189±45 (n=22), respectively; P<0.05 comparing banded versus sham-operated animals. We observed no significant differences in the K⁺ currents between the 2 groups of animals at 4 and 8 weeks. However, banded animals exhibited a significant increase in Na⁺ and Na⁺-Ca²⁺ exchange current densities compared with controls. Furthermore, we have found a significant attenuation in the Ca²⁺-dependent inactivation of the L-type Ca²⁺ current in the banded compared with sham-operated animals, likely as a result of the significant downregulation of the sarcoplasmic reticulum Ca²⁺ ATPase, which has been documented previously in the heart failure animals. Our data provide an alternate mechanism for APD prolongation in cardiac hypertrophy and failure and support the notion that there is close interaction between Ca²⁺ handling and action potential profile.