Inhibition of Catecholamine Secretion from Bovine Chromaffin Cells by Adenine Nucleotides and Adenosine

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Abstract
ATP, ADP, and adenosine have been found to inhibit acetylcholine-stimulated secretion from isolated cells of bovine adrenal medulla (chromaffin cells). Maximal inhibition is −30% under the conditions studied; half-maxmal inhibition occurs at nucleotide concentration in the micromolar range. Cells must be incubated with ATP for -90 s for maximal inhibition, but inhibition by adenosine occurs much faster, an observation suggesting the possibility that ATP and ADP exert their effect after being converted to adenosine. Experiments with cells preloaded with the fluorescent calcium chelator quin 2 indicate that external ATP can diminish the rise in cytosolic Ca2+ concentration that follows stimulation by acetylcholine.