Altered expression and activity of G-proteins, mitogen activated protein kinases, and tyrosine kinases in aging kidney cortex

Background: Renal function declines with age and this may be related to cha nges in the expression or activity of various signal transduction proteins in the kidney. Methods: The present study compared the expression and activity of G(alpha i(1-3)) and G(alpha s) phosphorylation of mitogen activated protein kinases (MAP-K) (44 and 42 kd) and the activity of tyrosine kinase in renal cortic al homogenates of young (4-month-old) and aging (14-month-old) rats. Results: The GTP/(GTP+GDP) binding ratio of G(alpha s) was significantly de creased in the kidney cortex of aging rats compared to young rats, while th e GTP/(GTP+GDP) binding ratio of G(alpha i(1-3)) increased significantly in kidney cortex of aging rats. Tyrosine kinase activity and phosphorylation of MAP-K (44 and 42 kd) were also reduced in the kidney cortex of aging rat s compared to young rats. Conclusions: These results suggest that diminished phosphorylation of MAP-K and tyrosine kinase activity as well as changes in the binding of GTP/(GTP +GDP) to G(alpha i(1-3)) and G(alpha s) may contribute to the age-related d ecline in renal tubular and vascular function seen in aging animals.