RELATIONSHIP OF ABNORMAL INTRACELLULAR CALCIUM MOBILIZATION TO MYOCYTE HYPERTROPHY IN HUMAN VENTRICULAR MYOCARDIUM

Objective: Calcium transients in muscles from patients with end stage heart failure consist of two components (L1 and L2) at physiological extracellular calcium concentrations ([Ca2+]o; the second component (L2) can appear in normal human myocardium at high [Ca2+]o. In muscles from end stage heart failure patients L2 is associated with significant hypertrophy, To expand these observations a group of muscles from control patients with mild hypertrophy but without overt heart disease was studied (n=8), in which a second calcium transient component was present during high [Ca2+]o. Methods: Using the ratio of the two components of the calcium transient (L2/L1) seen in trabeculae from heart failure patients as a marker of intracellular calcium mobilisation, the hypothesis was tested that the extent of abnormality in transsarcolemmal calcium flux, and/or sarcoplasmic reticular calcium release and reuptake, correlates with the degree of hypertrophy present. Results: In contrast to non-hypertrophied myocardium, hypertrophied myocardium from patients without heart failure often showed an increase in the L2/L1 ratio at higher [Ca2+]o. Hypertrophied myocardium from patients with failure showed a progressive increase in the L2/L1 ratio, reflecting further impairment of calcium mobilisation. There was a positive correlation between the degree of hypertrophy and calcium mobilisation alterations that was enhanced by raised [Ca2+]o. Altered [Ca2+]i mobilisation may develop early in the course of hypertrophy, before the onset of clinical signs of cardiac dysfunction.