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

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.