Decrease in Gs protein expression may impair adenylate cyclase activation in old kidneys.
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.
Gerontology Research Center, National Institute on Aging, National Institutes of Health, Baltimore 21224.
C T
CT
Liang
J
J
Barnes
H
H
Hanai
M A
MA
Levine
D000262:Adenylyl Cyclases / Q000378:metabolism*; D000375:Aging / Q000378:metabolism*; D000818:Animals; D015152:Blotting, Northern; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism*; D008297:Male; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014158:Transcription, Genetic
D012333:RNA, Messenger; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases