Activation of TRPC Channel Currents in Iron Overloaded Cardiac Myocytes.

Abstract

Background - Arrhythmias and heart failure are common cardiac complications leading to substantial morbidity and mortality in patients with hemochromatosis, yet mechanistic insights remain incomplete. We investigated the effects of iron (Fe) on electrophysiological properties and intracellular Ca2+ (Ca2+i) handling in mouse left ventricular cardiomyocytes. Methods - Cardiomyocytes were isolated from the left ventricle of mouse hearts and were superfused with Fe3+/8-hydroxyquinoline complex (5-100 μM). Membrane potential and ionic currents including transient receptor potential canonical (TRPC) was recorded using the patch-clamp technique. Ca2+i was evaluated by using Fluo-4. Cell contraction was measured with a video-based edge detection system. The role of TRPCs in the genesis of arrhythmias was also investigated by using a mathematical model of a mouse ventricular myocyte with the incorporation of the TRPC component. Results - We observed prolongation of the action potential (AP) duration and induction of early and delayed afterdepolarizations (EADs and DADs) in myocytes superfused with 15 µM Fe3+/8-hydroxyquinoline (8-HQ) complex. Iron treatment decreased the peak amplitude of the L-type Ca2+ current (ICa,L) and total K+ current (IK), altered Ca2+i dynamics, and decreased cell contractility. During the final phase of Fe treatment, sustained Ca2+i waves (CaWs) and repolarization failure occurred and ventricular cells became unexcitable. Gadolinium abolished CaWs and restored the resting membrane potential (RMP) to the normal range. The involvement of TRPC activation was confirmed by ITRPC recordings in the absence or presence of functional TRPC channel antibodies. Computer modeling captured the same AP and Ca2+i dynamics and provided additional mechanistic insights. Conclusions - We conclude that iron overload induces cardiac dysfunction that is associated with TRPC channel activation and alterations in membrane potential and Ca2+i dynamics.