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  • Title: Stable inhibition of adenylate cyclase by muscarinic agonist in rat parotid gland: effects of neomycin and pertussis toxin.
    Author: Hatta S, Ohshika H.
    Journal: Res Commun Chem Pathol Pharmacol; 1991 Apr; 72(1):53-68. PubMed ID: 1647049.
    Abstract:
    Treatment of rat parotid slices with carbachol (CCh) resulted in the stable inhibition of isoproterenol-induced activation of adenylate cyclase (AC); the inhibition of the enzyme was persistently observed in washed membrane prepared from parotid slices pretreated with CCh. Methoxamine, but not clonidine, also caused stable inhibition. Activation of AC by 5'-guanylylimidodiphosphate (GppNHp) and by NaF was also attenuated by treatment with either CCh or methoxamine, indicating reduction of the Gs protein function. Pertussis toxin treatment prevented CCh-induced inhibition of the enzyme. However, MnCl2-stimulated and forskolin-stimulated activity, and the inhibition of forskolin-stimulated activity by GppNHp were not altered by CCh treatment. It appears, therefore, that the stable muscarinic inhibition of AC involves the Gi protein, but it does not result from the inhibitory regulation of AC activity by the interaction between the Gi protein and the catalytic unit of AC. Furthermore, the inhibition of GppNHp-stimulated AC activity by CCh was effectively reversed by the pretreatment of slices with neomycin. This suggests that the stimulation of phosphoinositide hydrolysis elicited by CCh possibly participates in stable muscarinic inhibition of AC presumably by reducing the function of the Gs protein. Thus, in the rat parotid gland, CCh appears to cause a stable inhibition of AC through two different mechanisms; one is associated with the Gi protein and the other is associated with the stimulation of phosphoinositide metabolism.
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