Interactions between Ca2+- and cAMP-dependent stimulatory pathways in parietal cells

Isolated rat parietal cells were used to investigate the role of intracellular Ca 2+ in the action of cAMP-dependent secretagogues and cross talk between cAMP- and Ca 2+ -dependent stimulatory pathways. Aminopyrine accumulation (an index of acid produced and trapped by the parietal cells), cytosolic free Ca 2+ , morphological transformation and cell viability were used to investigate parietal cell function and stimulation. The increase of cytosolic free Ca 2+ promoted by gastrin, or carbachol, was abolished by the intracellular Ca 2+ chelator 1,2-bis(2-aminophenoxy)ethane- N,N,N′,N′ -tetraacetic acid (BAPTA, 10 μM). Also, the morphological transformations induced by dibutyryladenosine 3′:5′-cyclic monophosphate (DBcAMP), gastrin, and S p-adenosine-cyclic-3′,5′-monophosphothioate ( S p-cAMPS) were completely abolished by BAPTA (10 μM). In aminopyrine accumulation the action of 1 mM DBcAMP was dose-dependently reduced by BAPTA. The Ca 2+ ionophore A23187 alone, in the range of 1 pM to 1 μM, had no effect but it dose-dependently potentiated the action of 1 mM DBcAMP in aminopyrine accumulation. The inhibitory actions of BAPTA on DBcAMP- and histamine-stimulated aminopyrine accumulation were dose-dependently reversed by A23187. Histamine-stimulated protein kinase activity and viability parameters as cellular lactate dehydrogenase (LDH) and trypan blue exclusion were not changed by BAPTA. These results indicated that in isolated parietal cells: (1) the action of cAMP-dependent secretagogues in aminopyrine accumulation and morphological transformation are dependent on cytosolic free Ca 2+ ; (2) Ca 2+ -induced morphological transformation is essential for aminopyrine accumulation; (3) a threshold level of one second messenger is required for stimulation of aminopyrine accumulation by the other second messenger.