AJP - Renal Physiology, Vol 264, Issue 5 770-F773, Copyright © 1993 by American Physiological Society
Decrease in Gs protein expression may impair adenylate cyclase activation in old kidneys
C. T. Liang, J. Barnes, H. Hanai and M. A. Levine
Gerontology Research Center, National Institute on Aging, National Institutes of Health, Baltimore 21224.
The possibility that alteration in stimulatory guanine nucleotide-binding
protein (Gs) expression may contribute to the blunting of renal parathyroid
hormone (PTH)-stimulated adenylate cyclase in aged rats was examined. Using
rat cDNA probe, we identified a Gs alpha-subunit (Gs alpha) of 1.9 kb. Age
did not alter the size of Gs alpha mRNA. The level of Gs alpha mRNA
[normalized to poly(A)+ RNA] was decreased 23%, which was consistent with
our previous report that Gs alpha protein decreased in senescence. In
contrast, mRNA level of Gi alpha 2 increased with age. Level of beta-actin
mRNA did not change with age. Nuclear runoff assay was performed to
determine the transcription rate of Gs mRNA. Synthesis of poly(A)+ RNA and
total RNA was reduced 39% and 37%, respectively, in nuclei prepared from
old kidney, which suggested a general decline in RNA synthesis capacity in
old rats. Our results also showed the transcription rate of Gs alpha mRNA
in aged rats was reduced 89%, a decrease far exceeding that observed for
total RNA or poly(A)+ RNA. We concluded that the decrease in steady-state
level of Gs alpha mRNA was specific and probably was due to a reduction in
the transcription activity. Thus alteration in Gs transcription may
contribute, at least in part, to the impaired renal adenylate cyclase
activation in aged rats.
