ADENOSINE UPTAKE BY CHOLINERGIC SYNAPTOSOMES FROM TORPEDO ELECTRIC ORGAN

Pure cholinergic synaptosomes prepared from the electric organ of Torpedo are able to take adenosine up efficiently and convert it to ATP. The apparent K_m of the adenosine uptake is 2.4 μM and the V_m: 518 pmol/30′/mg prot. The uptake system exhibits a high specificity towards adenosine, as shown by the lack of competition with analogues. Tubercidin blocks the uptake competitively and dipyridamole is a very potent non competitive inhibitor (K_i= 4 × 10^-8 M). Considering that during nerve activity ATP is released extracellularly and can modulate transmitter release, the physiological significance of adenosine uptake is discussed as a possible mechanism to terminate the ATP action.