Location and function of transient receptor potential canonical channel 1 in ventricular myocytes

Abstract

Transient receptor potential canonical 1 (TRPC1) protein is abundantly expressed in cardiomyocytes. While TRPC1 is supposed to be critically involved in cardiac hypertrophy, its physiological role in cardiomyocytes is poorly understood. We investigated the subcellular location of TRPC1 and its contribution to Ca 2+ signaling in mammalian ventricular myocytes. Immunolabeling, three-dimensional scanning confocal microscopy and quantitative colocalization analysis revealed an abundant intracellular location of TRPC1 in neonatal rat ventricular myocytes (NRVMs) and adult rabbit ventricular myocytes. TRPC1 was colocalized with intracellular proteins including sarco/endoplasmic reticulum Ca 2+ ATPase 2 in the sarcoplasmic reticulum (SR). Colocalization with wheat germ agglutinin, which labels the glycocalyx and thus marks the sarcolemma including the transverse tubular system, was low. Super-resolution and immunoelectron microscopy supported the intracellular location of TRPC1. We investigated Ca 2+ signaling in NRVMs after adenoviral TRPC1 overexpression or silencing. In NRVMs bathed in Na + and Ca 2+ free solution, TRPC1 overexpression and silencing was associated with a decreased and increased SR Ca 2+ content, respectively. In isolated rabbit cardiomyocytes bathed in Na + and Ca 2+ free solution, we found an increased decay of the cytosolic Ca 2+ concentration [Ca 2+ ] i and increased SR Ca 2+ content in the presence of the TRPC channel blocker SKF-96365. In a computational model of rabbit ventricular myocytes at physiological pacing rates, Ca 2+ leak through SR TRPC channels increased the systolic and diastolic [Ca 2+ ] i with only minor effects on the action potential and SR Ca 2+ content. Our studies suggest that TRPC1 channels are localized in the SR, and not present in the sarcolemma of ventricular myocytes. The studies provide evidence for a role of TRPC1 as a contributor to SR Ca 2+ leak in cardiomyocytes, which was previously explained by ryanodine receptors only. We propose that the findings will guide us to an understanding of TRPC1 channels as modulators of [Ca 2+ ] i and contractility in cardiomyocytes.

A comprehensive overview of the complex world of the endo- and sarcoplasmic reticulum Ca2+-leak channels

“…In the latter, TRPC1 functions as a Ca 2+ -leak channel, increasing the [Ca 2+ ] cyt at rest and during muscle activation [122]. The same function is described in cardiomyocytes, where TRPC1 is mainly expressed in the SR and is associated with a decreased SR Ca 2+ content [123].…”

Fibroblast Growth Factor 23 Stimulates Cardiac Fibroblast Activity through Phospholipase C-Mediated Calcium Signaling

“…Upregulation of TRPC1 contributed to the development of cardiac hypertrophy [ 34 , 35 ]. TRPC1 might regulate Ca 2+ leakage from the ER in neonatal rat ventricular myocytes [ 36 ]. However, it remains unclear whether TRPC1 plays a role in modulating Ca 2+ signaling in cardiac fibroblasts.…”

Calcium and Heart Failure: How Did We Get Here and Where Are We Going?

“…This suggested that not only the Ca 2+ released from SR and Ca 2+ mobilized by the NCX, but Ca 2+ from another source might be involved. These Ca 2+ channels may later have been identified to be transient receptor potential canonical (TRPC) channels [ 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 ], which have been reported to mediate store-operated Ca 2+ entry (SOCE) and mechano-electrical feedback in the cardiomyocyte [ 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 ]. Moreover, the mechanistic link between TRPCs and Ca 2+ mishandling has been reported in multiple experimental models of cardiac disease including myocardial infarction [ 66 , 81 , 82 , 83 , 84 , 85 , 86 , 87 ], atrial fibrillation [ 88 , 89 , 90 , 91 ], and iron overload cardiomyopathy [ 92 ].…”