Activation of calcium-sensing receptor increases TRPC3 expression in rat cardiomyocytes

Transient receptor potential (TRP) channels are expressed in cardiomyocytes, which gate a type of influx of extracellular calcium, the capacitative calcium entry. TRP channels play a role in mediating Ca(2+) overload in the heart. Calcium-sensing receptors (CaR) are also expressed in rat cardiac tissue and promote the apoptosis of cardiomyocytes by Ca(2+) overload. However, data about the link between CaR and TRP channels in rat heart are few. In this study, reverse transcriptase polymerase chain reaction (RT-PCR) and Western blotting were used to examine the expression of the TRP canonical proteins TRPC1 and TRPC3 in adult and neonatal rat cardiomyocytes. Laser scan confocal microscopy was used to detect intracellular [Ca(2+)](i) levels in isolated adult rat ventricular myocytes. The results showed that, in adult rat cardiomyocytes, the depletion of Ca(2+) stores in the endoplasmic/sarcoplasmic reticulum (ER/SR) by thapsigargin induced a transient increase in [Ca(2+)](i) in the absence of [Ca(2+)](o) and the subsequent restoration of [Ca(2+)](o) sustained the increased [Ca(2+)](i) for a few minutes, whereas, the persisting elevation of [Ca(2+)](i) was reduced in the presence of the TRPC inhibitor SKF96365. The stimulation of CaR by its activator gadolinium chloride (GdCl(3)) or spermine also resulted in the same effect and the duration of [Ca(2+)](i) increase was also shortened in the absence of [Ca(2+)](o). In adult and neonatal rat cardiomyocytes, GdCl(3) increased the expression of TRPC3 mRNA and protein, which were reversed by SKF96365 but not by inhibitors of the L-type channels and the Na(+)/Ca(2+) exchangers. However, GdCl(3) had no obvious effect on the expression of TRPC1 protein. These results suggested that CaR stimulation induced activation of TRP channels and promoted the expression of TRPC3, but not TRPC1, that sustained the increased [Ca(2+)](i).