Scientific article

Inhibition of evoked acetylcholine release: two different mechanisms in the Torpedo electric organ

Published inEuropean journal of pharmacology, vol. 133, no. 2, p. 225-234
Publication date1987

The action of agents inhibiting evoked transmitter release was investigated by analysing the Ca2+ secretion relationship, electrophysiologically and biochemically, and by measuring the stimulation-induced 45Ca accumulation in the tissue. Transmitter release saturated at external Ca2+ concentrations higher than 4 mM, the releasing mechanism probably being the limiting step. Antagonists of Ca2+ entry (Mg2+, Cd2+, diltiazem) decreased the sensitivity of acetylcholine release to Ca2+, acting as competitive inhibitors, and reduced the stimulation-induced 45Ca accumulation. Quinacrine produced similar effects, indicating that it interacts primarily with Ca2+ entry. In contrast, oxotremorine and adenosine depressed transmitter release proportionally at all Ca2+ concentrations, acting as non-competitive inhibitors, and did not modify the stimulation-induced 45Ca accumulation. Their inhibitory effects were additive and reflected a decrease in the quantal content of the responses evoked. It is concluded that both drugs inhibit cholinergic transmission in the electric organ without altering Ca2+ entry into the nerve endings.

  • Acetylcholine/ secretion
  • Adenosine/pharmacology
  • Animals
  • Calcium/ metabolism
  • Calcium Channel Blockers/pharmacology
  • Electric Organ/ drug effects/innervation/metabolism
  • Electric Stimulation
  • Ion Channels/ drug effects/physiology
  • Magnesium/pharmacology
  • Oxotremorine/pharmacology
  • Quinacrine/pharmacology
  • Torpedo
Citation (ISO format)
MULLER, Dominique, LOCTIN, F., DUNANT, Yves. Inhibition of evoked acetylcholine release: two different mechanisms in the Torpedo electric organ. In: European journal of pharmacology, 1987, vol. 133, n° 2, p. 225–234. doi: 10.1016/0014-2999(87)90154-3
ISSN of the journal0014-2999

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