EFFECT OF DIADENOSINE POLYPHOSPHATES ON CATECHOLAMINE SECRETION FROM ISOLATED CHROMAFFIN CELLS

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. The evoked secretory response to diadenosine polyphospates had an absolute requirement for extracellular Ca2+. 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. 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.