FACILITATION OF [H-3] ACH RELEASE BY FORSKOLIN DEPENDS ON A(2)-ADENOSINE RECEPTOR ACTIVATION

The effect of forskolin (FSK) on [H-3]-acetylcholine release ([H-3]-ACh) from the phrenic motor nerve terminals, and its modification by adenosine deaminase (ADA), by the A2-adenosine receptor agonist 2-[p-(2-carboxyethyl)phenethylamino]-5'-N-ethylcarboxamide adenosine (CGS 21680C), by the A1-adenosine receptor agonist R-N6-phenylisopropyl adenosine (R-PIA), by the A2-antagonist N-(2-(dimethylamino)-ethyl)-N-methyl-4-(2,3,6,7-tetrahydro-2,6-dioxo-1,3-dipropyl-1H-purine-8-yl)-benzene sulphonamide (PD 115,199), and by the A1-antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) were studied on the rat phrenic-hemidiaphragm preparation. It is concluded that the excitatory effect of FSK on evoked [H-3]-ACh release depends on tonic A2-adenosine receptor activation.