LAUSR

Transient receptor potential cation (TRPC) 1 channels are thought to play a role in store-operated and receptor-operated calcium entry in various mammalian cell types. However, our understanding of the functional role of these channels in cardiomyocytes remains to be ill-defined. Here, we test the hypothesis that the channels are involved in calcium leak from the sarcoplasmic reticulum (SR) and modulate the cytosolic calcium concentration in cardiomyocytes. Our studies were performed on neonatal rodent ventricular myocytes. After cell isolations, cells were plated on glass slides. Two days after isolation cells were infected with adenoviral vectors of TRPC1 tagged with eGFP. Measurements were performed 4-5 days after infection. Immunolabeling, three-dimensional scanning confocal microscopy and quantitative colocalization analysis revealed an abundant intracellular density of native TRPC1 and TRPC1 expressed via adenoviral vectors. TRPC1 was not associated with the sarcolemma, but the SR. We measured the rest decay and caffeine induced peak calcium release using rapid scanning confocal microscopy on infected cells loaded with the calcium sensitive dye Rhod-3. We found an increased SR calcium content in the presence of the TRPC channel blocker SKF-96365. SR calcium content exhibited a decreasing relationship with TRPC1 expression. In a computational model, activated SR TRPC1 channels increased the systolic and diastolic cytosolic calcium concentration with only minor effects on action potential and SR calcium content. Our studies indicate that TRPC1 channels are not involved in sarcolemmal electrophysiology of rodent ventricular myocytes, but localized in the SR. The studies support our hypothesis that the channels play a role as SR calcium leak channels. The findings could guide us to an understanding of TRPC channels as physiological modulators of intracellular calcium and contractility in cardiac myocytes.