1030-11 Ventricular Myocytes in Culture Express Endothelin-1 (ET-1) mRNA but not ET-2 mRNA or ET-3 mRNA in Response to the Hypertrophic Agonists Phenylephrine and ET-1

Abstract

In addition to its potent vasoactive properties, endothelin-l (El1) has powerful effects on cell growth and may be involved in the process of myocardial hypertrophy. The roles of ET-2 and ET-3 in this process are unknown. We have investigated the effects of exogenous ET-l and the α-adrenergic agonist phenylephrine (PEP) on levels of ET-l, ET-2 and ET-3 mRNAs in myocytes. Neonatal rat ventricular myocytes were stimulated with ET-l or PEP Quantitative ribonuclease protection assay and laser densitometry were used to assay levels of the mRNAs for ET-l, ET-2 and ET-3, and constitutive GAPDH. ET-l mRNA was present in unstimulated myocytes. ET-2 and ET-3 mRNAs were not detectable in control or stimulated myocytes. ET-l and PEP caused a dose-dependent increase in myocyte [ET-l mRNA] relative to [GAPDH mRNA] within 1 hour, [ET-l mRNA] remained elevated to 24 hours: Myocyte [ET-l mRNA], optical density units time (hours) 0 0.5 1 6 24 Control 0.07 ± 0.03 0.18 ± 0.02 0.06 ± 0.03 0.17 ± 009 0.19 ± 010 ET-l, 0.1 μM 0.22 ± 0.07 0.66 ± 0.18 * 0.87 ± 0.20 * 0.97 ± 0.18 * PEP, 100 μM 013 ± 0.04 0.59 ± 0.12 * 0.94 ± 0.09 ‡ 0.89 ± 0.21 * means ± sem, n = 3, * p < 0.05 ‡ p < 0.005, relative to control Ventricular myocytes produce ET-l mRNA but not ET-2 or ET-3 mRNAs. PEP and ET-l increase ET-l mRNA levels in myocytes. PEP-induced hypertrophy may be mediated at least in part by ET-l generation from myocytes.