OVEREXPRESSION OF G(S-ALPHA) PROTEIN IN THE HEARTS OF TRANSGENIC MICE

Alterations in beta-adrenergic receptor-G(s)-adenylyl cyclase coupling underlie the reduced catecholamine responsiveness that is a hallmark of human and animal models of heart failure, To study the effect of al tered expression of G(s alpha), we overexpressed the short isoform of G(s alpha) in the hearts of transgenic mice, using a rat alpha-myosin heavy chain promoter. G(s alpha) mRNA levels were increased selectivel y in the hearts of transgenic mice, with a level 38 times the control, Despite this marked increase in mRNA, Western blotting identified onl y a 2.8-fold increase in the content of the G(s alpha) short isoform, whereas G(s) activity was increased by 88%, The discrepancy between G( s alpha) mRNA and G(s alpha) protein levels suggests that the membrane content of G(s alpha) is posttranscriptionally regulated. The steady- state adenylyl cyclase catalytic activity was not altered under either basal or stimulated conditions (GTP + isoproterenol, GTP gamma S, NaF , or forskolin). However, progress curve studies did show a significan t decrease in the lag period necessary for GppNHp to stimulate adenyly l cyclase activity, Furthermore, the relative number of beta-adrenergi c receptors binding agonist with high affinity was significantly incre ased, Our data demonstrate that a relatively small increase in the amo unt of the coupling protein G(s alpha) can modify the rate of catalyst activation and the formation of agonist high affinity receptors.