PHYSIOLOGY SHORT- AND LONG-LATENCY EFFECTS OF 15-HYDROXYEICOSATETRAENOIC ACID ON EXTINCTION OF THE ACETYLCHOLINE-INDUCED INWARD CURRENT IN Helix lucorum NEURONS A. S. Pivovarov, E. I. Drozdova, Yu. Yu. Belosludtsev, P. M. Demin, and G. I. Myagkova UDC 612.822.3.014.46:[615.31:547.295.96].08 KEY WORDS: 15-hydroxyeicosatetraenoic acid; plasticity of acetylcholine receptors; Helix lucorum neurons Enzymic oxidation of arachidonic acid by lipoxygenases gives a large of products (eicosanoids), including polyunsat- urated hydroperoxy- and hydroxy (mono- and di-) fatty acids, leukotrienes, and other compounds [4]. Lipoxygenase oxida- tion can take several different courses depending on the type and positional specificity of the enzymes [4]. Oxidation of arachidonic acid by the action of 15-1ipoxygenase (15-LO) leads to the formation of 15(S)-hydroperoxy-5Z, 8Z, llZ, 13E-eicosatetraenoic acid, which is further reduced to 15(S)-hydroxy-5Z, 8Z, llZ, 13E-eicosatetraenoic acid (15-HETE). Just as for other eicosanoids, it probably has a signal function in the cell. Considering that activation of muscarinic acetylcholine receptors induces oxidation of arachidonic acid [3], involvement of 15-HETE in the regulation of acetylcho- line receptors and their plasticity cannot be ruled out. The aim of this investigation was to study the role of 15-HETE in short-term plasticity of acetylcholine receptors of Helix lucorum neurons. EXPERIMENTAL METHOD Experiments were carried out on identified neurons RPa3 and LPa3 of Helix lucorum taurica Kryn in a preparation of isolated ganglia at room temperature. The circumesophageal nerve ring was fixed in a continuous flow chamber with a volume of I ml. After treatment of the preparation with 2% collagenase solution (type IA, from "Sigma," USA) in Ringer's solution for 30 min at room temperature, the connective-tissue membranes covering the ganglia were removed. Ringer's solution of the following composition (in mM) flowed through the chamber containing the preparation: NaC1 100, KCI 4, CaCI 2 10, MgC12 4, Tris-HC1 10, pH 7.5. Transmembrane currents were recorded, using a method of voltage clamping on the membrane by two electrodes. The intracellular microelectrodes were drawn from "Pyrex" glass and filled with KCI (2.5 M), the resistance of the microelectrodes being 10-38 Mf~ (21.4 ___ 2.5 Mr2, M ___ m). A double-barreled micropipet was applied to the outer surface of the soma. The iontophoretic channel was filled with acetylcholine (ACh) chloride ("Serva," West Germany) in distilled water (4 M, pH 7.4), the balancing channel with 2 M NaCI. Cationic currents (580-740 nA, 3-8 sec, 3.5 ___ 0.4~ were passed through the iontophoretic channel. The resistance of the pipets was 20-30 MfL The series included 11-13 successive iontophoretic applications of ACh by a current of constant direction, strength, and duration. The first 10 stimuli were applied at intervals of 60-90 sec (67.5 __+3.1) to extinguish the ACh-current. Subsequent stimuli were applied at intervals of 10 min to assess the degree and rate of recovery of the extinguished reaction. The experiment consisted of several series of extinction -- control (before the action of drugs), experimental, and recovery. During the series Department of Higher Nervous Activity, M. V. Lomonosov Moscow State University. Department of Chemistry and Technology of Fine Organic Compounds, M. V. Lomonosov Moscow Institute of Fine Chemical Technology. (Present- ed by Academician of the Academy of Medical Sciences of the USSR I. P. Ashmarin.) Translated from Byulleten' l~ksperi- mental'noi Biologii i Meditsiny, Vol. 112, No. 7, pp. 3-5, July, 1991. Original article submitted December 17, 1990. 0007-4888/91/0007-0893512.50 9 Plenum Publishing Corporation 893