Adenylyl cyclase and G protein receptor kinase expression during development of heart failure

We examined alterations in left ventricular (LV) G protein receptor kinase (GRK) and adenylyl cyclase (AC) isoform expression during the development of pacing-induced congestive heart failure (CHF). AC isoform and GRK expression were assessed 4 (mild CHF) and 28 (severe CHF) days after initiation of pacing. LV β-adrenergic receptor (β-AR) number and G protein content were unchanged by mild CHF. LV AC isoform mRNA content was unaltered by mild CHF, but there were increases in total GRK activity (P < 0.01), total GRK5 protein content (P < 0.04), and GRK5 mRNA (P = 0.003); total GRK2 protein content and GRK2 mRNA were unchanged. Mild CHF was associated with decreased β-AR coupling (P < 0.01) and reduced β-AR stimulation of AC (P < 0.05). Severe CHF was associated with LV β-AR downregulation (P = 0.0001) and uncoupling (P < 0.001) and marked generalized reduction of AC activity (mean P = 0.01). LVAC(VI) isoform mRNA content was reduced (P = 0.002), but AC(II) and AC(v) isoform mRNA contents were unaffected. Persistent elevations in LV total GRK activity (P < 0.01), total GRK5 protein content (P < 0.001), and GRK5 mRNA (P = 0.01) were found; in contrast, total GRK2 protein content was unchanged and GRK2 mRNA was reduced (P = 0.02). These studies indicate that increased GRK activity is an early change in heart failure that predates alterations in AC isoform expression. Impaired hormonal stimulation of AC, associated with β-AR uncoupling, may result from increased GRK5 expression. AC downregulation is isoform specific and accompanies severe but not mild CHF.