Ionic dependence of adenosine uptake by isolated nerve endings from Torpedo electric organ

Pure cholinergic synaptosomes from the electric organ of Torpedo marmorata have a saturable adenosine uptake mechanism (calculated K_m, 3 μM; V_max, 24 pmol/min/mg prot.). In this preparation, high intracellular calcium elicited by increasing external calcium concentration, potassium depolarization, sodium-calcium exchange inhibition or divalent cation ionophore A23187 action, inhibits adenosine uptake into synaptosomes. The data presented in this paper are consistent with the interpretation that high intracellular calcium participates in the regulation of the high-affinity adenosine uptake system.