The role of calcium in the cyclic AMP response to histamine in rabbit cerebral cortical slices

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Abstract
1 The effect of calcium on the H1-and H2-receptor components of the cyclic AMP response to histamine in rabbit cerebral cortical slices has been investigated. 2 Removal of calcium ions from the incubation medium during the preparation, preincubation and final incubation of brain slices significantly reduced the cyclic AMP responses to adenosine, histamine and the H2-selective agonist, impromidine. 3 Removal of calcium ions from the incubation medium during only the final incubation with agonists did not influence the responses to adenosine, histamine, impromidine and the H1-selective agonist, 2-thiazolylethylamine. 4 Final incubation of rabbit cerebral cortical slices in calcium-free buffer containing EGTA (1 mm) however, selectively reduced the cyclic AMP responses to the H1-agonists histamine and 2-thiazolylethylamine without affecting the response to impromidine or adenosine. 5 These latter incubation conditions significantly reduced the maximal extent of the augmentation of impromidine-or adenosine-stimulated cyclic AMP accumulation produced by H1-receptor stimulation, without affecting the EC50 values of the H1-agonists. Calcium-free/EGTA conditions did not, however, alter the dose-response parameters for the response to the H2-agonist, impromidine. 6 These data provide further evidence that the two histamine receptor systems affect cyclic AMP accumulation in rabbit cerebral cortical slices by different mechanisms.