Altered coupling of alpha 1-adrenergic receptor-G protein in rat parotid during aging.
A possible role for altered signal transduction mechanisms in impaired alpha 1-adrenergic-stimulated secretory function during aging was investigated in parotid cells prepared from adult (6 mo) and old (24 mo) rats. Compared with adults, epinephrine-stimulated 45Ca2+ efflux and inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] production were reduced 31 and 36% in cells of old rats, respectively. There was a highly significant correlation between 45Ca2+ efflux and Ins(1,4,5)P3 production. In saponin-permeabilized cells, no significant differences in Ins(1,4,5)P3-stimulated 45Ca2+ efflux in adult and old preparations were observed. When G proteins were stimulated by guanosine 5'-O-(3-thiotriphosphate) or NaF, no age differences in Ins(1,4,5)P3 production were detected. Stimulation of phosphoinositide-specific phospholipase C (PLC) by CaCl2 in adult and old cells was also comparable. Moreover, no differences in immunolabeled common alpha (GTP binding site), Gi alpha, PLC-gamma, or PLC-delta could be detected in either cytosol or membranes of adult and old preparations. In the absence of 5'-guanylylimidodiphosphate [Gpp(NH)p], no age-related changes in epinephrine competition for [3H]prazosin binding sites were observed. Approximately 30% of the agonist binding sites existed in a high-affinity form at both ages. Gpp(NH)p caused large rightward shifts of epinephrine displacement curves in adult membranes (converting all binding sites to the low-affinity form), but not old. Moreover, epinephrine was much more effective in stimulating G protein low-Km GTPase in parotid membranes from adult than old rats. These data suggest that age-related impairments in alpha 1-adrenergic responsiveness are mediated, at least in part, by the functional alterations in the coupling of G proteins with alpha 1-adrenergic receptors.
Miyamoto
A
A
Molecular Physiology and Genetics Section, National Institute on Aging, National Institutes of Health, Francis Scott Key Medical Center, Baltimore, Maryland 21224.
Villalobos-Molina
R
R
Kowatch
M A
MA
Roth
G S
GS
D000375:Aging / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D004837:Epinephrine / Q000494:pharmacology; D020558:GTP Phosphohydrolases / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism / Q000502:physiology; D008297:Male; D008566:Membranes / Q000378:metabolism; D010306:Parotid Gland / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism
D011942:Receptors, Adrenergic, alpha; D015544:Inositol 1,4,5-Trisphosphate; D010738:Type C Phospholipases; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D002118:Calcium; D004837:Epinephrine