Clinical evidence points to the possibility that patients with hypertrophic cardiomyopathy (HCM) may have disordered regulation of cytosolic calcium. We hypothesized that these patients might have an increased number of calcium channels so that for a given signal, they have increased calcium influx. Such an increased number of calcium channels has recently been reported in the Syrian hamster model of cardiomyopathy. To study calcium channel density in human myocardium we have been using right atrial appendages isolated during cardiac surgery on patients with or without HCM. We now have evidence to suggest that patients with hypertrophic cardiomyopathy have elevated levels of Ca+2 antagonist binding sites (thought to be equivalent of calcium channels) compared to other patients undergoing cardiac surgery. This increase appears to be selective as there is no increase in sodium-fast channels or B-receptors. The levels of Ca+2 antagonist binding sites in the right atrial appendage correlate well with those in the septum of patients with HCM. These findings suggest that an increased number of calcium channels may play an important role in the pathophysiology of this disease.
