A Ca2+-linked increase in coupled cAMP synthesis and hydrolysis is an early event in cholinergic and beta-adrenergic stimulation of parotid secretion.

Abstract

The dynamics and compartmental characteristics of cAMP metabolism were examined by 180 labeling of cellular adenine nucleotide a phosphoryls in rat parotid gland stimulated to secrete with .8-adrenergic and cholinergic agents.The secretory response occurred in association with a rapidly increased rate ofcAMP hydrolysis apparently coordinated with an equivalent increase in the rate of cAMP synthesis, since the cellular concentration of cAMP remained unchanged. The magnitude of this metabolic response was equivalent to the metabolism of 10-75 times the cellular content of cAMP within the first minute of stimulation. This increased metabolic rate occurred only during the early (1-3 min) period of stimulation, in what appeared to be an exclusive cellular compartment distinguished by a unique distribution of 180 among adenine nucleotide a phosphoryls. This '"0 distribution contrasted with that produced by forskolin, which increased cellular cAMP concentration and elicited only a delayed response missing the early secretory component. The early acceleration of cAMP metabolism appeared linked to a stimulus-induced increase in intracellular Ca2" concentration, since the Ca2" ionophore ionomycin produced the same metabolic response in association with secretion. These observations suggest that cAMP metabolism is involved in stimulus-secretion coupling by a Ca2"-linked mechanism different from that in which cAMP plays the role of a second messenger.coordinated with equivalent increased rates of cAMP synthesis with little or no change occurring in cellular concentration of the cyclic nucleotide. Support for this suggested "non-second-messenger" involvement of cyclic nucleotides has been obtained from studies of cGMP metabolism in vertebrate photoreceptors (8-10). To identify the occurrence of a cyclic nucleotide metabolic system of this type, a procedure has been developed to measure stimulus-induced changes in the dynamics of cyclic nucleotide metabolism in intact cells (11 To determine the total amount of cAMP hydrolyzed in a period of time, the content of 180 in the a phosphoryls ofall the adenine 5'-nucleotides must, therefore, be measured. In this report experiments are described in which this procedure was used to determine the changes in the dynamics of cAMP metabolism in rat parotid gland related to stimulus-secretion coupling.The primary intracellular mediator of 8-adrenergic-stimulated amylase release from the rat parotid gland is thought to be cAMP (1). However, in a number of reports, 83-adrenergic stimulation of amylase release has been dissociated from any elevation of cellular cAMP concentration. For example, low concentrations of isoproterenol stimulate amylase release without detectable increases in total tissue cAMP content (2). The 8-adrenergic agonists salbutamol and 1-(4-hydroxyphenyl)-2-isopropylaminoethanol (PI-39) stimulate amylase secretion without increasing cellular cAMP content at any concentration of either secretogogue (2, 3). Also, carbachol can promote amylase secretion without incre...

Synergistic Inhibition of Vascular Smooth Muscle Cell Migration by Phosphodiesterase 3 and Phosphodiesterase 4 Inhibitors

“…First, a coordinated regulation of PKA activity by adenylyl cyclase and cAMP-PDE activities could influence the steady-state concentration of cAMP required for full activation of PKA in cells in a manner independent of absolute cAMP levels. 52 In support of this model, Deeg et al 53 demonstrated that parotid gland amylase secretion was stimulated by a coordinated increase in both adenylyl cyclase and PDE activity such that the cells seemed to respond to an increase in cAMP metabolism even though the levels of cAMP did not change. In addition, subcellular colocalization of selected PDE and PKA isoforms may allow for a coordinated regulation of function.…”

Characterization of cAMP‐dependent protein kinase activation by CCK in rat pancreas

“…Secondly, it is possible that an increase in the metabolic cycling of cAMP (which is revealed under conditions of phosphodiesterase inhibition) is capable of activating this enzyme in the absence of a measurable increase in the total cellular level of cAMP. Such a metabolic cycling of cAMP has been reported to mediate early amylase secretion in the rat parotid gland [18]. Thirdly, since this assay measures net substrate phosphorylation, it is possible that mechanisms independent of cAMP-dependent protein kinase activity may influence total substrate phosphorylation.…”

Secretion of α‐amylase in human parotid gland epithelial cell culture

“…Chronic administration of ISP-induced cellular hypertrophy and hyperplasia of acinar cells in the parotid glands (Yashiro et al, 1987). Similarly, P-adrenergic agonist stimulated a-amylase secretion in the rat parotid gland, which was accompanied by intracellular accumulation of CAMP (Ito et al, 1981;Deeg et al, 1988;Baldys-Waligorska et al, 1987;Snowdowne et al, 1989;McKinney et al, 1989). In a human submandibular tumor cell line, ISP was shown to stimulate cAMP production (Marmary et al, 1989).…”