Dynamic changes in G alpha i-2 levels in rat hearts associated with impaired heart function after myocardial...

The objective of this study was to determine if levels and function of Gs alpha and G alpha i-2 in rat hearts change over time following acute myocardial infarction (MI), and if so, whether the changes in G proteins are associated with changes in heart function. As compared with sham-operated controls, the G alpha i-2 level of MI rats did not change at day 1, increased by 64% at day 3 (P < 0.01) and by 55% at day 9 (P < 0.05) accompanied by reduced adenylyl cyclase activity, and returned to control by day 21. By contrast, the Gs alpha level did not change at any time. Cardiac function in MI animals was markedly impaired at days 1, 3, and 9 as evidenced by substantial elevation in LVEDP and reduction in maximum rates of pressure development and relaxation, and was partially restored at day 21. Increased G alpha i-2 level in MI rats correlated significantly to severity of impaired cardiac function. The results show a three-phase dynamic pattern in G alpha i-2 level following acute MI: a lag phase, an increased expression phase associated with marked impairment of heart function, and a late phase in which the expression returns to control level accompanied by partially restored cardiac function.