Aldosterone- and testosterone-mediated intracellular calcium response in skeletal muscle cell cultures

Fast nongenomic steroid actions in several cell types seem to be mediated by second messengers such as intracellular calcium ([Ca2+](i)) and inositol 1,4,5-trisphosphate (IP3). We have shown the presence of both slow calcium transients and IP3 receptors associated with cell nuclei in cultured skeletal muscle cells. The effect of steroids on [Ca2+](i) was monitored in Fluo 3-acetoxymethyl ester-loaded myotubes by either confocal microscopy or fluorescence microscopy, with the use of out-of-focus fluorescence elimination. The mass of IP3 was determined by radioreceptor displacement assay. [Ca2+](i) changes after either aldosterone (10-100 nM) or testosterone (50-100 nM) were observed; a relatively fast (