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

AbstractIsolated rat parietal cells were used to investigate the role of intracellular Ca2+ in the action of cAMP-dependent secretagogues and cross talk between cAMP- and Ca2+-dependent stimulatory pathways. Aminopyrine accumulation (an index of acid produced and trapped by the parietal cells), cytosolic free Ca2+, morphological transformation and cell viability were used to investigate parietal cell function and stimulation. The increase of cytosolic free Ca2+ promoted by gastrin, or carbachol, was abolished by the intracellular Ca2+ 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 Sp-adenosine-cyclic-3′,5′-monophosphothioate (Sp-cAMPS) were completely abolished by BAPTA (10 μM). In aminopyrine accumulation the action of 1 mM DBcAMP was dose-dependently reduced by BAPTA. The Ca2+ 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 Ca2+; (2) Ca2+-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