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Activators of Protein Kinase C Act at a Postreceptor Site to Amplify Cyclic AMP Production in Rat Pinealocytes
Author(s) -
Sugden David,
Klein David C.
Publication year - 1988
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1988.tb13242.x
Subject(s) - protein kinase c , pinealocyte , protein kinase a , forskolin , medicine , endocrinology , phorbol , phosphodiesterase , ibmx , pertussis toxin , isoprenaline , biology , cholera toxin , stimulation , chemistry , g protein , signal transduction , kinase , receptor , biochemistry , enzyme , pineal gland , melatonin
Activation of α 1 ‐adrenoceptors appears to amplify β‐adrenergic stimulation of cyclic AMP (CAMP) accumulation in rat pinealocytes severalfold by a mechanism involving activation of a Ca 2+ ‐, phospholipid‐dependent protein kinase (protein kinase C). The mechanism of action of protein kinase C was investigated in this report using intact cells. Activation of protein kinase C with 4β‐phorbol 12‐myristate 13‐acetate (PMA; 10 −7 M ) or the α 1 ‐adrenergic agonist phenylephrine (PE; 10 −6 M ) did not inhibit cAMP efflux in β‐adrenergically stimulated cells. The amplification of the β‐adrenergic cAMP response by these agents also occurred in the presence of isobutylmethylxanthine (10 −3 M ) and Ro 20–1724 (10 4‐ M ), an observation suggesting that inhibition of cAMP phosphodiesterase activity is not the mechanism of action. Furthermore, although PMA (10 7 ‐ M ) caused a sixfold increase in the magnitude of the cAMP response to isoproterenol, it did not alter the EC 50 of the response (1.7 × 10 −8 M ), a result indicating that protein kinase C activation does not alter β‐adrenoceptor sensitivity. The cAMP response following cholera toxin pretreatment (60–120 min) was rapidly and markedly enhanced by a,‐adrenergic agonists (cirazoline > PE > methoxamine), by phorbol esters (PMA > 4β‐phorbol 12,13,‐dibutyrate >> 4α‐phorbol 12,13‐didecanoate), and by synthetic diacylglycerols (1,2‐dioctanoylglycerol > 1‐oleoyl 2‐acetylglycerol >> diolein). The cAMP response to forskolin (10 −5 M ) was also increased by PE (3 × 10 −6 M ) and PMA (10 −7 M ). Together, these observations indicate that protein kinase C activation amplifies β‐adrenergic stimulation of pinealocyte cAMP production at a site beyond the receptor, perhaps on a regulatory guanine nucleotide binding protein or adenylyl cyclase itself.