Altered calcium handling in experimental pressure-overload hypertrophy in the ferret.

The purpose of this study was to evaluate the relationship between changes in the intracellular handling of free, ionized calcium and the functional alterations that occur in cardiac hypertrophy. We developed a model of right ventricular pressure-overload hypertrophy in the ferret by critical banding of the pulmonary artery; this method produced significant degrees of hypertrophy within 1-3 months of surgery. We removed papillary muscles, 1 mm or less in diameter, from ferrets with cardiac hypertrophy and their age- and weight-matched controls, and loaded them with the bioluminescent calcium indicator, aequorin, in order to record intracellular calcium transients. Compared to the controls, the hypertrophied muscles demonstrated a prolonged duration of isometric contraction but a marked decrease in peak isometric tension development. The increased duration of isometric contraction in the hypertrophied muscles correlated with a similar prolongation of the calcium transient; we interpret this to mean that the rate of sequestration and perhaps release of calcium by intracellular stores is decreased in hypertrophy. In contrast, the amplitudes of the calcium transients were similar in muscles from both groups of ferrets, indicating that the diminution in peak tension developed by the hypertrophied muscles was not due to decreased availability of activator calcium. We conclude that the prolonged time course of tension development, but not the diminished peak isometric tension response, may be related to changes in intracellular calcium handling.