Expression and functional characterization of SCaMPER: a sphingolipid-modulated calcium channel of cardiomyocytes

Abstract

Calcium channels are important in a variety of cellular events including muscle contraction, signaling, proliferation, and apoptosis. Sphingolipids have been recognized as mediators of intracellular calcium release through their actions on a calcium channel, sphingolipid calcium release-mediating protein of the endoplasmic reticulum (SCaMPER). The current study investigates the expression and function of SCaMPER in cardiomyocytes. Northern analyses and RT-PCR cloning and sequencing revealed SCaMPER expression in both human and rat cardiac tissue. Immunofluorescence and Western blot analyses demonstrated that SCaMPER is abundant in cardiac tissue and is localized to the sarcotubular junction. This was confirmed by the colocalization of SCaMPER with dihydropyridine and ryanodine receptors by confocal microscopy. Purified T tubules were shown to contain SCaMPER and immunoelectron micrographs suggested that SCaMPER is located to the junctional T tubules, but a junctional SR localization cannot be ruled out. The sphingolipid ligand for SCaMPER, sphingosylphosphorylcholine (SPC), initiated calcium release from the cardiomyocyte SR. Importantly, antisense knockdown of SCaMPER mRNA produced a substantial reduction of sphingolipid-induced calcium release, suggesting that SCaMPER is a potentially important calcium channel of cardiomyocytes.