Role of tumour necrosis factor-a in the regulation of T-type calcium channel current in HL-1 cells

Increasing evidence indicates that inflammation contributes to the initiation and perpetuation of atrial fibrillation (AF). Although tumour necrosis factor (TNF)- levels are increased in patients with AF, the role of TNF- in the pathogenesis of AF remains unclear. Besides L-type Ca2+ currents (I-Ca,I-L), T-type Ca2+ currents (I-Ca,I-T) also plays an important role in the pathogenesis of AF. This study was designed to use the whole-cell voltage-clamp technique and biochemical assays to explore if TNF- is involved in the pathogenesis of AF through regulating I-Ca,I-T in atrial myocytes. It was found that compared with sinus rhythm (SR) controls, T-type calcium channel (TCC) subunit mRNA levels were decreased, while TNF- expression levels were increased, in human atrial tissue from patients with AF. In murine atrial myocyte HL-1 cells, after culturing for 24h, 12.5, 25 and 50ng/mL TNF- significantly reduced the protein expression levels of the TCC 1G subunit in a concentration-dependent manner. The peak current was reduced by the application of 12.5 or 25ng/mL TNF- in a concentration-dependent manner (from -15.08 +/- 1.11 pA/pF in controls to -11.89 +/- 0.83 pA/pF and -8.54 +/- 1.55 pA/pF in 12.5 or 25ng/mL TNF- group respectively). TNF- application also inhibited voltage-dependent inactivation of I-Ca,I-T,I- shifted the inactivation curve to the left. These results suggest that TNF- is involved in the pathogenesis of AF, probably via decreasing I-Ca,I-T current density in atrium-derived myocytes through impaired channel function and down-regulation of channel protein expression. This pathway thus represents a potential pathogenic mechanism in AF.