ENDOTHELIN-1 AS A PUTATIVE MODULATOR OF GENE-EXPRESSION AND CELLULAR PHYSIOLOGY IN CULTURED HUMAN CORPORAL SMOOTH-MUSCLE CELLS

Purpose: Increases in cytosolic calcium levels trigger smooth muscle c ontraction while nuclear calcium increases are thought to regulate gen e expression. Endothelin-1 (ET-1) affects both. The goal of these stud ies was to further investigate the importance of ET-1 to corporal phys iology by examining its actions on proliferation and immediate early g ene (IEG) expression in cultured human corporal smooth muscle cells. M aterials & Methods: Early passage (1-3) smooth muscle cells were grown in culture and exposed to either phenylephrine (PE) or ET-1 in the ab sence and presence of serum, the ETA or ETB selective antagonist BQ123 or IRL1038, or the L-type Ca2+ channel blocker, verapamil. Cell proli feration was assessed with a hemocytometer. The effects of ET-1 on c-m yc and c-fos were evaluated using Northern blot analysis. Parametric o r nonparametric statistics were used as appropriate. Results: Addition of ET-1 (100 nM) to serum-starved cultured corporal smooth muscle cel ls was associated with a nearly 2-fold increase in cell number, as wel l as 2 to 6-fold increases in c-myc and c-fos levels. Cellular prolife ration was inhibited by ETA- or ETB-receptor subtype blockade with BQ1 23 (1 mu M) Or IRL1038 (1 mu M), respectively, or blockade of Ca2+ cha nnels with verapamil (10 mu M). PE (3 mu M) had no detectable effect o n smooth muscle proliferation. Conclusions: Cell proliferation was med iated 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 observatio ns to indicate the potential pleotropic actions of this peptide in the regulation of human corporal smooth muscle physiology in vivo.