Testosterone Induces an Intracellular Calcium Increase by a Nongenomic Mechanism in Cultured Rat Cardiac Myocytes

Abstract

Androgens are associated with important effects on the heart, such as hypertrophy or apoptosis. These responses involve the intracellular androgen receptor. However, the mechanisms of how androgens activate several membrane signaling pathways are not fully elucidated. We have investigated the effect of testosterone on intracellular calcium in cultured rat cardiac myocytes. Using fluo3-AM and epifluorescence microscopy, we found that exposure to testosterone rapidly (1-7 min) led to an increase of intracellular Ca2+, an effect that persisted in the absence of external Ca2+. Immunocytochemical analysis showed that these effects occurred before translocation of the intracellular androgen receptor to the perinuclear zone. Pretreatment of the cells with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethylester and thapsigargin blocked this response, suggesting the involvement of internal Ca2+ stores. U-73122, an inhibitor of phospholipase C, and xestospongin C, an inhibitor of inositol 1,4,5-trisphosphate receptor, abolished the Ca2+ signal. The rise in intracellular Ca2+ was not inhibited by cyproterone, an antagonist of intracellular androgen receptor. Moreover, the cell impermeant testosterone-BSA complex also produced the Ca2+ signal, indicating its origin in the plasma membrane. This effect was observed in cultured neonatal and adult rat cardiac myocytes. Pertussis toxin and the adenoviral transduction of beta- adrenergic receptor kinase carboxy terminal peptide, a peptide inhibitor of betagamma-subunits of G protein, abolished the testosterone-induced Ca2+ release. In summary, this is the first study of rapid, nongenomic intracellular Ca2+ signaling of testosterone in cardiac myocytes. Using various inhibitors and testosterone-BSA complex, the mechanism for the rapid, testosterone-induced increase in intracellular Ca2+ is through activation of a plasma membrane receptor associated with a Pertussis toxin-sensitive G protein-phospholipase C/inositol 1,4,5-trisphosphate signaling pathway.

Prenatal androgen exposure causes hypertension and gut microbiota dysbiosis

“…104 , 105 The upregulation of androgen receptor that we observed within the PNA heart may alter the electrophysiology of the cardiomyocytes of the left ventricle by altering expression of receptors involved in the regulation of membrane potential. 106 , 107 Androgens may promote the development of cardiomyopathy by upregulating potassium channel regulatory subunits and reducing cardiomyocyte repolarization. 108 , 109 Indeed, the enlarged walls and decreased cross-sectional area of the left ventricle in the PNA animals resembles early-stage concentric cardiac hypertrophy, although mRNA expression of markers of cardiac hypertrophy were unchanged in PNA animals.…”

Testosterone enhances estradiol's cardioprotection in ovariectomized rats

“…Zhang et al (2011) found that testosterone suppresses oxidative stress via androgen receptor-independent pathway in murine cardiomyocytes. In cultured cardiac myocytes, testosterone induced a rapid and nongenomic intracellular Ca 2C release through activation of a plasma membrane androgen receptor associated with the PTX-sensitive G protein-phospholipase C/IP3 signaling pathway (Vicencio et al 2006). Bourghardt et al (2010) found that testosterone atheroprotection was androgen receptor-dependent as well as androgen receptor-independent in male mice.…”

Cardiovascular Effects of Androgens

“…Activation of this pathway facilitates the hydrolysis of phosphatidylinositol 4,5-bisphosphate by phospholipase C, thereby generating diacylglycerol and IP 3 . IP 3 mediates opening of IP 3 receptors in the sarcoplasmatic reticulum, which in turn produce rapid (1-5 min) Ca 2+ release (Vicencio et al, 2006). Similar effects of testosterone have been identified in T-cells, skeletal muscle and neuroblastoma cells (Benten et al, 1999;Estrada et al, 2003Estrada et al, , 2006.…”

“…However, these responses involve the generation of different patterns of Ca 2+ signals and also in the activation of complementary Ca 2+ -dependent pathways. Thus, in addition to the classical mechanism of steroid action in cardiac cells, androgens activate additional specific signal transduction pathways (Altamirano et al, 2009;Vicencio et al, 2006). An interesting hypothesis is that these second messenger cascades may ultimately serve to modulate the transcriptional activity of the intracellular androgen receptor and its associated global response.…”

“…It has been described that testosterone induces intracellular Ca 2+ increase through a nongenomic action mechanism, as we discussed earlier in this chapter. Studies in cultured cardiomyocytes show that through a nongenomic mechanism, testosterone is implicated in the activation of a membrane receptor coupled to a G q protein, thus resulting in the production of IP 3 and Ca +2 release from endoplasmic reticulum (Vicencio et al, 2006). Then, calcium oscillations induce the activation of the mitogen-activated protein kinase ERK 1/2, which in turns phosphorylates mTOR, promoting hypertrophic cardiac growth (Altamirano et al, 2009).…”