Quantitative determination of pertussis toxin-sensitive G proteins using [32P]ADP-ribosylation in human platelet membranes: negative correlation with ages

Epinephrine- and thrombin-stimulated high-affinity GTPase activity in platelet membranes from patients with psychiatric disorders

Although heterotrimeric guanine nucleotide-binding regulatory (G) proteins have been implicated in the pathophysiology of mental illnesses (especially mood disorders), direct evidence has been scarce. This study was designed to reveal possible abnormalities of receptor-coupled G protein function in platelets in patients with psychiatric disorders such as depression and schizophrenia. The functional status of alpha(2A)-adrenergic receptor-coupled G(i2) and thrombin receptor-coupled G proteins (G(i2)+G(q)) was determined by the increase in high-affinity GTPase activity in response to epinephrine and thrombin, respectively, in platelet membranes from 18 patients with mood disorders (15 unipolar and three bipolar subtype), 13 schizophrenic patients, four neurotic patients and 29 healthy control subjects. Neither alpha(2A)-adrenergic receptor-coupled G(i2) nor thrombin receptor-coupled G(q) was functionally altered in platelets from psychiatric patients compared with control subjects. No significant correlation was observed between these biochemical measures in platelets and severity of psychopathological symptoms. The functional coupling efficiency of G proteins with receptors appears intact, at least between alpha(2A)-adrenergic receptors and G(i2), and between thrombin receptors and G(q), in platelets from patients with psychiatric disorders.

Platelet pertussis toxin-sensitive G proteins in affective disorders

Pertussis toxin (islet-activating protein, IAP) sensitive guanine nucleotide-binding regulatory (G) proteins were quantitatively determined using [32P]ADP-ribosylating response in the platelet membranes prepared from patients with affective disorders (3 bipolar, 10 major depression) and sex- and age-matched controls. IAP-catalyzed [32P]ADP-ribosylation was not significantly different between patients and controls, suggesting that the quantity of IAP-sensitive G proteins is unaltered in affective disorder patients. The implication of this result was discussed with special reference to the previous reports dealing with the role of G proteins in affective disorders.

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

Previously we have reported an increased renal alpha 1- and beta-adrenergic receptor expression in male spontaneously hypertensive rats that occurred ontogenetically 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 alpha-subunits of the G proteins Gs (Gs short and Gs long), G(i), and Gq by immunoblotting and pertussis toxin-catalyzed ADP-ribosylation in renal membranes from 3-, 6-, 8-, and 28-week-old normotensive and spontaneously hypertensive male Wistar-Kyoto rats; additionally, 28-week-old female normotensive and spontaneously hypertensive rats were studied. During ontogenesis of male normotensive rats, Gs short increased, Gs long remained unchanged, and G(i) alpha and Gq alpha decreased. In adult normotensive rats no sex differences were detected for Gs short, Gs long, and G(i) alpha. When male rats from the normotensive and spontaneously hypertensive strains were compared, all G protein alpha-subunits were similar in the prehypertensive phase (3 weeks). In established hypertension (28 weeks), Gs long and Gq alpha were reduced, whereas Gs short and G(i) alpha remained unchanged. Gs long was also reduced during the development of hypertension (6 and 8 weeks), whereas Gs short and G(i) alpha were not consistently altered in this phase. The reduction in Gs long seen in male adult hypertensive rats was not detectable in female hypertensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological characterization of epinephrine-stimulated GTPase activity in human platelet membranes

The alpha 2-adrenergic receptor-mediated stimulation of GTPase activity was investigated in human platelet membranes. The stimulatory effect of (-)-epinephrine was strictly dependent on Mg2+ and derived from a high-affinity GTPase activation. (-)-Epinephrine and (-)-norepinephrine stimulated GTPase activity in a concentration-dependent manner with EC50 values of 200 and 600 nM, respectively. These effects were stereospecific, since (+/-)-epinephrine, (+/-)-norepinephrine, and (+)-epinephrine were less potent in stimulating the enzyme activity with EC50 values of 4, 1 and 3 microM, respectively. Thrombin also stimulated GTPase activity concentration dependently with an EC50 value of 0.02 U/mL. The maximal effects of (-)-epinephrine, (-)-norepinephrine, and thrombin were not additive in any combination. Clonidine did not stimulate GTPase activity, whereas another synthetic alpha 2-adrenergic agonist, p-aminoclonidine, had the characteristics of a partial agonist. The rank order of potency for antagonists to inhibit the activation of GTPase by 1 microM (-)-epinephrine was yohimbine = rauwolscine > idazoxan = oxymetazoline = phentolamine = WB4101 = (+)-mianserin > (-)-mianserin > prazosin > (-)-propranolol. Negative logarithms of the IC50 values of these antagonists corresponded well with the negative logarithmic values of Ki(pKi) for the alpha 2A-adrenergic receptors determined by a receptor-binding technique in human platelets. These results indicate that epinephrine stimulates high-affinity GTPase activity of G proteins (putatively Gi2), which are also coupled with thrombin receptors, in a Mg(2+)-dependent and stereospecific manner, via alpha 2A-adrenergic receptor activation in human platelet membrane preparations.