Effect of diadenosine polyphosphates on catecholamine secretion from isolated chromaffin cells

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.