Effect of diadenosine polyphosphates on catecholamine secretion from isolated chromaffin cells

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Abstract
1 The action of several diadenosine polyphosphates (AP3A, AP4A and AP5A) on basal, and on nicotine-and high K+-evoked, catecholamine (CA) release has been investigated. Each of the three diadenosine polyphosphates weakly but significantly increased basal CA secretion. This enhancement represented about 10% of the response evoked by 2 μm nicotine. 2 The evoked secretory response to diadenosine polyphosphates had an absolute requirement for extracellular Ca2+. 3 In contrast, these compounds had an inhibitory action on nicotine-evoked release. This response was concentration-dependent, EC50 values being 3.2 ± 0.4 μm, 4.0 ± 1.6 μm and 19.3 ± 4.0 μm for AP3A, AP4A, and AP5A, respectively. The lower the concentration of nicotine used to evoke secretion, the higher the inhibitory power of these compounds. 4 The CA secretion evoked by K+-rich solutions was further enhanced by AP3A and AP5A, whereas AP4A inhibited it. The possible physiological role of these dual actions is discussed.