Sulfhydryl G Proteins and Phospholipase A2-Associated G Proteins Are Involved in Adrenergic Signal Transduction in the Rat Pineal Gland

• Published in: General and comparative endocrinology 2001-06, Vol.122 (3), p.320-328
• Main Authors: Gupta, Braj B.P., Spessert, Rainer, Rimoldi, Stefan, Vollrath, Lutz
• Format: Article
• Language: English
• Subjects: arylalkylamine N-acetylransferase; cAMP; cGMP; G proteins; rat pineal gland
• ISSN: 0016-6480; 1095-6840
• DOI: 10.1006/gcen.2001.7645

The rat pineal gland with its circadian noradrenaline-regulated melatonin rhythm is an excellent model for studying adrenergic signal transduction with respect to cAMP and cGMP formation. The stimulatory Gs proteins play a well-established role in this process. In contrast, the potential roles of the inhibitory Gi proteins, the functionally unclear other Go proteins, and a number of G protein subtypes are not known. The present study examines the effects on β1- and β1-plus-α1-stimulated cAMP and cGMP formation of a number of G protein modulators in rat pinealocyte suspension cultures. The effects of the nitric oxide donor sodium nitroprusside on cGMP were also examined. The results showed that drugs that activate G proteins of the Gi/Go family, i.e., pertussis toxin, mastoparan, and compound 48/80, had no effect on unstimulated, isoproterenol (β1)-stimulated, or combined isoproterenol/phenylephrine (β1-plus-α1)-stimulated cAMP and cGMP accumulation. However, in this experimental paradigm, the inhibitors of sulfhydryl G proteins (N-ethylmaleimide) and those of phospholipase A2-related G proteins (isotetrandrine) exerted a clear inhibitory effect. Sodium-nitroprusside-stimulated cGMP accumulation was also inhibited. These results confirm a previous report that members of the Gi/Go family, which are present in the rat pineal gland, do not play a major role in adrenergic signal transduction. The new finding that sulfhydryl G proteins and phospholipase A2-associated G proteins exert a clear stimulatory effect on adrenergic signal transduction suggests that they are subtypes of Gs proteins.