Increases in cytosolic calcium levels trigger smooth muscle contraction while nuclear calcium increases are thought to regulate gene expression. Endothelin-1 (ET-1) affects both. The goal of these studies was to further investigate the importance of ET-1 to corporal physiology by examining its actions on proliferation and immediate early gene (IEG) expression in cultured human corporal smooth muscle cells.Materials & Methods
Early passage (1-3) smooth muscle cells were grown in culture and exposed to either phenylephrine (PE) or ET-1 in the absence and presence of serum, the ETA or ETB selective antagonist BQ123 or IRL1038, or the L-type Ca2+ channel blocker, verapamil. Cell proliferation was assessed with a hemocytometer. The effects of ET-1 on c-myc and c-fos were evaluated using Northern blot analysis. Parametric or nonparametric statistics were used as appropriate.Results
Addition of ET-1 (100 nM) to serum-starved cultured corporal smooth muscle cells was associated with a nearly 2-fold increase in cell number, as well as 2 to 6-fold increases in c-myc and c-fos levels. Cellular proliferation was inhibited by ETA- or ETB-receptor subtype blockade with BQ123 (1 micro M) or IRL1038 (1 micro M), respectively, or blockade of Ca2+ channels with verapamil (10 micro M). PE (3 micro M) had no detectable effect on smooth muscle proliferation.Conclusions
Cell proliferation was mediated by activation of the ETA and ETB receptor subtypes, dependent on transmembrane Ca2+ flux, and correlated with significant increases in c-myc and c-fos mRNA levels. These studies extend previous observations to indicate the potential pleotropic actions of this peptide in the regulation of human corporal smooth muscle physiology in vivo.