Objective: The immunosuppressive drug Cyclosporine A (CsA) is a key substance in pharmacological therapy following solid organ transplantation and has been suggested to prevent cardiac hypertrophy. We investigated the direct effects of CsA on myocardial function, because these are largely unknown.
Methods: In multicellular cardiac muscle preparations from end-stage failing and non-failing human hearts as well as from non-failing rabbit hearts we investigated the effects of CsA on contractile performance, sarcoplasmic reticulum (SR) Ca2+-load, cytosolic calcium transients, calcium sensitivity of the myofilaments, and myocardial oxygen consumption.
Results: In failing human muscle preparations there was a concentration dependent decrease in contractile force; the maximal effect amounted to 55.6+/-6.4% of control while EC50 was reached at 1.0+/-0.3 nM (n=6). These concentrations are at and even below the therapeutic plasma levels. CsA decreased the aequorin light signal in human failing trabeculae to 71.5+/-5.9% (n=5), indicating decreased calcium transients. Estimation of the SR calcium load via measurement of rapid cooling contractures revealed a decrease to 84.4+/-6.5% in failing human preparations (n=6). Measurements of both decreased SR calcium load and force development in presence of CsA were also observed in four non-failing human muscle preparations. In rabbit muscle preparations (n=8), developed force decreased to 50.2+/-7.7% (n=8, EC50: 1.9+/-0.4 nM) and rapid cooling contractures to 74.0+/-7.4% of control at 100 nmol/l CsA. No direct effects were observed on myofilament calcium sensitivity nor on maximal force development of permeabilized preparations from the rabbit (n=7). Oxygen consumption measurements showed that CsA decreased the economy of contraction to 76.4+/-7.9% in rabbit preparations (n=8).
Conclusions: CsA causes a direct cardio-depressive effect at clinically relevant concentrations, most likely due to altered handling of Ca2+ by the SR.