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

Abstract

] i was monitored in Fluo 3-acetoxymethyl esterloaded myotubes by either confocal microscopy or fluorescence microscopy, with the use of out-of-focus fluorescence elimination. The mass of IP 3 was determined by radioreceptor displacement assay. [Ca 2ϩ ] i changes after either aldosterone (10-100 nM) or testosterone (50-100 nM) were observed; a relatively fast (Ͻ2 min) calcium transient, frequently accompanied by oscillations, was evident with both hormones. A slow rise in [Ca 2ϩ ] i that reached its maximum after a 30-min exposure to aldosterone was also observed. Calcium responses seem to be fairly specific for aldosterone and testosterone, because several other steroid hormones do not induce detectable changes in fluorescence, even at 100-fold higher concentrations. The mass of IP 3 increased transiently to reach two-to threefold the basal level 45 s after addition of either aldosterone or testosterone, and the IP 3 transient was more rapid than the fast calcium signal. Spironolactone, an inhibitor of the intracellular aldosterone receptor, or cyproterone acetate, an inhibitor of the testosterone receptor, had no effect on the fast [Ca 2ϩ ] i signal or in the increase in IP 3 mass. These signals could mean that there are distinct nongenomic pathways for the action of these two steroids in skeletal muscle cells. steroid hormones; inositol 1,4,5-trisphosphate; calcium waves; nongenomic pathway STEROID HORMONES ARE CAPABLE of producing rapid (within 2 min) effects in several cell types (12,22,36). These rapid responses are not compatible with the classical mechanism of action proposed for these hormones, which involves binding to intracellular receptors, transcriptional processes, and protein synthesis (1, 20). Thus, for rapid steroid effects, the existence of membrane receptors for steroids has been proposed (2, 37). In skeletal muscle, steroid hormones have long been known to modulate gene expression, and hormones like testosterone have been related to both muscle hypertrophy (4, 25) and upregulation of a number of proteins (31). In particular, glucocorticoids and mineralocorticoids have been related to up-and downregulation, respectively, of sodium pumps in skeletal muscle (10), implying the presence of steroid hormone receptors in muscle cells. Because all these effects have been the result of chronic (hours to days) treatments, it would be interesting to know whether exposure to these hormones is also accompanied by fast nongenomic events.The signal transduction mechanism for the rapid action of steroids in some cellular models could be regulated by second messengers such as intracellular calcium ([Ca 2ϩ

Elevated Testosterone Induces Apoptosis in Neuronal Cells

“…Cultured cells were washed once with PBS before stimulation with testosterone (from concentrated stocks made in ethanol). The final ethanol concentration (Ͻ0.01%) had no effect on intracellular Ca 2ϩ concentration or biochemical determinations (32).…”

The TRPM8 Protein Is a Testosterone Receptor

“…1 and 2). Given that testosterone might be involved in several regulatory pathways, including inositol 1,4,5-triphosphate signaling (17) and G-protein coupled receptor (GPCR6A) regulation (16), the best evidence we provide in this work is direct activation of TRPM8 with testosterone in planar lipid bilayers (Figs. 7-9).…”

“…Testosterone Directly Activates TRPM8 Channels in Planar Lipid Bilayers-Steroids are involved in regulating various cellular processes and metabolic pathways (16,17). Therefore, it may be challenging to recognize direct channel activation based upon cellular responses, and more rigorous characterization is needed.…”

Androgen regulation of satellite cell function

“…Although no studies have examined potential nongenomic effects of androgens on myoblasts, non-genomic pathways have been observed in rat myotubes treated with androgens (Estrada et al 2000(Estrada et al , 2003. These effects were characterized by an early increase in intracellular calcium, triggered 15-30 s after testosterone addition, preceded by an increase in inositol 1,4,5-trisphosphate (IP3) mass (Estrada et al 2000).…”