Ontogenesis of sympathetic responsiveness in spontaneously hypertensive rats. II. Renal G proteins in male and female rats.

Abstract

Previously we have reported an increased renal a,-and /3-adrenergic receptor expression in male spontaneously hypertensive rats that occurred ontogeneticalry in parallel with blood pressure elevation. However, increased receptor numbers were not accompanied by enhanced stimulation of inositol phosphate and cyclic AMP formation, respectively, indicating relative desensitization. We have now quantified a-subunits of the G proteins G, (G, ,,"," and G, t^), G,, and G q by immunoblotting and pertussis toxin-catalyzed ADP-ribosylation in renal membranes from 3-, 6-, 8-, and 28-week-old normotensive and spontaneously hypertensive male WistarKyoto rats; additionally, 28-week-old female normotensive and spontaneously hypertensive rats were studied. During ontogenesis of male normotensive rats, G, &" increased, G, r emained unchanged, and G^ and G,,, decreased. In adult normotensive rats no sex differences were detected for G, ^^, G, k.,, and G^. When male rats from the normotensive and T he kidney is the tissue with the greatest long-term impact on blood pressure control because of its infinite gain mechanism. 1 On the other hand, chronically elevated arterial blood pressure affects renal function.2 -3 Renal function is tightly controlled by neurotransmitters and hormones such as catecholamines, angiotensin II, endothelin, vasopressin, and neuropeptide Y, many of which act via G proteins. -6 We have recently reported that in parallel with blood pressure elevations numbers of a t -, a 2 -, and /3-adrenergic receptors increase in kidneys of spontaneously hypertensive rats (SHR) relative to those of age-matched normotensive Wistar-Kyoto (WKY) rats.7 Despite increased a r and /3-adrenergic receptor numbers, norepinephrine-stimulated inositol phosphate formation and isoprenaline-stimulated cyclic AMP (cAMP) formation remained unchanged.7 These data suggest the occurrence of a relative desensitization of renal a r and £-adrenergic receptors during the development of hypertension in SHR./3-Adrenergic receptor coupling to cAMP formation by adenylate cyclase occurs via the stimulatory G protein G, and can be attenuated via the inhibitory G protein G ; .8 aj-Adrenergic receptor coupling to inositol phosphate formation appears to occur via G q and/or G n 9 ; additionally, one or more subtypes of a^-adrenergic receptors may couple to inositol phosphate formaReceived October 21, 1993; accepted in revised form January 24, 1994.From the Department of Medicine, University of Essen, Germany.Correspondence to Dr Martin C. Michel, Nephrol. Lab. IG 1, Klinikum, Hufelandstr 55, D-45122 Essen, Germany. spontaneously hypertensive strains were compared, all G protein a-subunits were similar in the prehypertensive phase (3 weeks). In established hypertension (28 weeks), G, ,"", and G,,, were reduced, whereas G, &,« and G^ remained unchanged. G, fco, was also reduced during the development of hypertension (6 and 8 weeks), whereas G, ^ and G^, were not consistently altered in this phase. The reduction in G, ^^ seen in male adult hypertens...

The long (Gs(alpha)-L) and short (Gs(alpha)-S) variants of the stimulatory guanine nucleotide-binding protein. Do they behave in an identical way?

“…While the levels of G s -L in membrane preparations prepared from 3-week-old and 28-week-old rats were roughly identical, the content of G s -S doubled in preparations from older animals (Michel et al 1994). Almost the opposite phenomenon has been observed in age-matched spontaneously hypersensitive rats; G s -S did not change, whereas G s -L significantly decreased in membranes derived from 28-week-old rats (Michel et al 1994). The reduced G s -L content may well be the molecular basis for the previously observed unchanged isoprenaline-stimulated cAMP formation despite the increased -adrenergic receptor number (Michel et al 1993).…”

“…The increase in the G s -L /G s -S ratio was found to be associated with an increase (Granneman et al 1990, Chaudry & Granneman 1991, Urasawa et al 1991 as well as a decrease in adenylate cyclase activity (Svoboda et al 1993, Kvapil et al 1995b, and the decrease in the G s -L /G s -S ratio was accompanied by an increase (Rius et al 1991, Kilgour & Anderson 1993, no change (Michel et al 1994) or a decrease (Green & Johnson 1989, Begin-Heick 1992 in the enzyme activity. More specifically, a dramatic increase in G s -S , accompanied by little or no change in G s -L , was found to proceed together with an increase (Walseth et al 1989, Rius et al 1991, Kilgour & Anderson 1993, no change (Michel et al 1994) or a decrease (Green & Johnson 1989) in adenylate cyclase activity.…”

“…The increase in the G s -L /G s -S ratio was found to be associated with an increase (Granneman et al 1990, Chaudry & Granneman 1991, Urasawa et al 1991 as well as a decrease in adenylate cyclase activity (Svoboda et al 1993, Kvapil et al 1995b, and the decrease in the G s -L /G s -S ratio was accompanied by an increase (Rius et al 1991, Kilgour & Anderson 1993, no change (Michel et al 1994) or a decrease (Green & Johnson 1989, Begin-Heick 1992 in the enzyme activity. More specifically, a dramatic increase in G s -S , accompanied by little or no change in G s -L , was found to proceed together with an increase (Walseth et al 1989, Rius et al 1991, Kilgour & Anderson 1993, no change (Michel et al 1994) or a decrease (Green & Johnson 1989) in adenylate cyclase activity. On the one hand this is not surprising, because the final effect of G s proteins on adenylate cyclase is modulated by other constituents of a complex G-protein-regulated signalling pathway (such as G i and G , to name just two) but, on the other hand, the lack of correlation between the G s -L /G s -S ratio and adenylate cyclase activity might indicate that the functional meaning of alternative splicing of pre-mRNA is not just regulation of coupling per se but regulation of some other process(es) not directly involved in the receptor-G-protein-adenylate cyclase-cAMP cascade.…”

“…To give some examples, G s -L markedly predominates in kidney, placenta, adrenal medulla, cortex and cerebellum (Evans et al 1986, Mumby et al 1986, Granneman & Kapatos 1990, Feinstein et al 1992, Michel et al 1994), whereas G s -S is the prevailing form in heart, liver, neostriatum and platelets (Mumby et al 1986, Molina y Vedia et al 1989, Cooper et al 1990, Kawai & Arinze 1996. The existence of different forms of G s with varying tissue distribution invites speculation that they may have evolved to perform different regulatory functions.…”

The decrease in the short variant of gsalpha protein is associated with an increase in [3H]CGP12177 binding, [3H]ouabain binding and Na, K-ATPase activity in brown adipose tissue plasma membranes of cold-acclimated hamsters

“…development, ageing and cellular differentiation) and pathophysiological (e.g. hepatectomy, alcoholism and genetic disorders) conditions , Rius et al 1991, Urasawa et al 1991, McFarlane-Anderson et al 1992, Ozawa et al 1993, Michel et al 1994, Viollet et al 1994, Yagami et al 1994, Denis-Henriot et al 1996, Kawai & Arinze 1996. This evidence, although descriptive and indirect, certainly promotes the idea that the expression of G s splice variants is regulated according to the functional needs of a given cell or tissue.…”