Stimulation-induced changes in cyclic nucleotide content by isolated rat parotid acini: effects of calcium

In the present study we investigated the relation between receptor activation and the acinar formation of cyclic nucleotides as a function of time, including effects of calcium. The experiments were performed using collagenase-isolated rat parotid acini and the cyclic nucleotide content was determined using a specific cAMP binding protein and cGMP antibody. Under physiological conditions, activation of beta-adrenoceptors increased cAMP content 27 fold within 60 sec. This response was not dependent upon the presence of extracellular calcium nor could it be mimicked by the calcium ionophore A23187. The adrenaline-induced activation of the alpha-adrenergic receptors lead to a 19% increase in cGMP content within 15 sec. This response was abolished in the absence of extracellular calcium. Pure activation of the alpha-1-adrenoceptors by phenylephrine resulted in a 62% increase in cGMP content within 15 sec. Finally, carbachol-induced activation of the cholinoceptors lead to a 50% transient increase in cGMP content within 7 sec. In the absence of calcium (EGTA present), the basal cGMP level was increased and in addition, the carbachol-induced cGMP formation was slower in onset and amounted to only 23% within 60 sec. The carbachol-induced cGMP formation could be mimicked by the calcium ionophore A23187 or by addition of calcium to acini preincubated in a calcium free buffer containing A23187. In conclusion, stimulation-induced formation of cyclic nucleotides under various conditions proved to be very rapid, well regulated, and sensitive processes.