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Action of suramin upon ecto‐apyrase activity and synaptic depression of Torpedo electric organ
Author(s) -
Martí Eulàlia,
Cantí Carles,
Aranda Immaculada Gómez,
Miralles Francesc,
Solsona Carles
Publication year - 1996
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1996.tb15528.x
Subject(s) - suramin , neurotransmission , acetylcholine , apyrase , neurotransmitter , purinergic receptor , biology , neuromuscular junction , endocrinology , adenosine , chemistry , medicine , neuroscience , biochemistry , receptor
1 The role of ATP, which is co‐released with acetylcholine in synaptic contacts of Torpedo electric organ, was investigated by use of suramin. Suramin [8‐(3‐benzamido‐4‐methylbenzamido)naphthalene‐1,3,5‐trisulphonic acid], a P 2 purinoceptor antagonist, potently inhibited in a non‐competitive manner the ecto‐apyrase activity associated with plasma membrane isolated from cholinergic nerve terminals of Torpedo electric organ. The K i was 30 μ m and 43 μ m for Ca 2+ ‐ADPase and Ca 2+ ‐ATPase respectively. 2 In Torpedo electric organ, repetitive stimulation decreased the evoked synaptic current by 51%. However, when fragments of electric organ were incubated with suramin the evoked synaptic current declined by only 14%. Fragments incubated with the selective. A 1 purinoceptor antagonist, DPCPX, showed 5% synaptic depression. 3 The effects of suramin and DPCPX on synaptic depression were not addictive. Synaptic depression may thus be linked to endogenous adenosine formed by dephosphorylation of released ATP by an ectoapyrase. The final effector in synaptic depression, adenosine, acts via the A 1 purinoceptor. 4 ATP hydrolysis is prevented in the presence of suramin. It slightly increased (20%) the mean amplitude of spontaneous miniature endplate currents. The frequency distribution of the amplitude of spontaneous events was shifted to the right, indicating that ATP, when not degraded, may modulate the activation of nicotinic acetylcholine receptors activated by the quantal secretion of acetycholine.