[Ionic mechanisms of the rapid (nicotinic) phase of the acetylcholine response of identified Planorbis neurons]. / Ionnye mekhanizmy bystroi (nikotinovoi) fazy atsetilkholinovogo otveta identifitsirovannykh neironov katushki.

The response to electrophoretic application of acetylcholine and suberyldicholine was studied in two identified neurons (LPed-2 and LPed-3) isolated from Planorbarius corneus left pedal ganglion. Acetylcholine reversal potential was found to be significantly more negative with K(2)SO(4)-filled microelectrodes than with KCl-filled ones. Reversal potentials for both acetylcholine and suberyldicholine were shifted in the depolarizing direction when Cl- in external medium was partly replaced by SO(2-)(4). These results suggest the Cl--dependence of both acetylcholine and suberyldicholine responses in LPed-2 and LPed-3. Both reversal potentials are identical (-50 mV) in LPed-3, whereas in LPed-2 the acetylcholine reversal potential was significantly less negative (-46 mV comparing to -62 mV). Partial substitution of sodium ions by tris shifted the acetylcholine reversal potential (but not the reversal potential of suberyldicholine) towards the hyperpolarization in LPed-2. Benzohexonium produced the same effect. The conclusion is made that in LPed-2 acetylcholine activates cholinoreceptors controlling Na;ermeability, besides cholinoreceptors responsible for Cl- permeability, whereas suberyldicholine activates selectively only cholinoreceptors controlling Cl- permeability.

[Demonstration of different type cholinoreceptors on the membrane of an isolated Planorbarius corneus mollusk membrane]. / Vyiavlenie kholinoretseptorov raznogo tipa na membrane izolirovannogo neirona molliuska Planorbarius corneus.

In experiments on isolated and identified neurones of the pedal ganglion of the gastropod mollusc P. corneus, it was demonstrated that biphasic response to ACh may be obtained both to superfusion and electrophoretic application. Fast (depolarizing) phase may be imitated by a nicotinomimetic drug, suberyldicholine, and blocked by d-tubocurarine. These data indicate that this phase results from activation of nicotinic cholinoreceptors. Slow (hyperpolarizing) phase may be evoked by a muscarinomimetic, dioxolane F-2268, which is taken as an indication of the muscarinic nature of cholinoreceptors responsible for this phase. Experiments on completely isolated neurones directly show that both kinds of cholinoreceptors belong to the same neurone. Biphasic pattern of the response depends on the level of the membrane potential and on the conditions of ACh application. The fast phase is more evident at membrane hyperpolarization, the slow one--at depolarization. The fast phase is more readily obtained by superfusion by high concentrations of ACh or at close position of electrophoretic micropipette to neuronal surface, whereas the slow phase may be easily obtained by superfusion with low concentrations of ACh or when the micropipette is not attached so closely to the cell.

[Sensitivity of the cholinoreceptive membrane of Lymnaea stagnalis neurons to mono- and bisquaternary ammonium compounds]. / Chuvstvitel'nost' kholinoretseptivnoi membrany neironov molliuska Lymnaea stagnalis k mono- i bischetvertichnym ammonievym soedineniiam.

The depolarizing potency of polymethylene-bis-trimethylammonium and alkyl-trimenthylammonium compounds with 3-10 methylene groups was studied on the identified giant central neurons of gastropod mollusc Limnaea stagnalis using intracellular microelectrode technique. The bisquaternary salts with 4-7 methylene groups were inactive while the mononitrogen analogues showed cholinomimetic activity. The similar results were obtained by other authors on Vertebrate skeletal muscles with substances studied. The possible explanations of this fact are suggested.

[Cholinergic mechanisms in the central nervous system of the sipunculoid Physcosoma japonicum]. / O kholinergicheskikh mekhanizmakh v tsentral'noi nervnoi sistems sipunkulidy Phycosoma japonicum

Acetylcholine (ACh) content of the central nervous system in the sipunculid P. japonicum was estimated by application of extracts from the nervous tissue to dental retractor of the sea urchin using ACh solutions with known concentration as a standard. It was shown that the nervous tissue contains 46 (from 41 to 51) microng of ACh (calculated as cation) per 1 g of wet material. In the presence of the nervous homogenate from Physcosoma, 880 micronM of ACh are hydrolyzed by 1 g of wet tissue per 1 hour. The content of ACh and the activity of cholinesterase are comparable with those in the brain of molluscs, arthropods and mammals. Anticholinesterase drugs (physostigmine and neostigmine) evoked spontaneous contractions of the proboscis retractor when applied to the nervous cord and enhanced the response of this muscle to electrical stimulation of this cord. Cholinolytics (arpenal and pentaphen) also caused spontaneous muscle contractions, but prevented the increase in muscular activity in response to electrical stimulation in presence of physotigmine. The data obtained suggest cholinergic nature of the transmission in the central nervous system of sipunculids.

Pharmacological study of two kinds of cholinoreceptors on the membrane of identified completely isolated neurones of Planorbarius corneus.

Completely isolated identified neurones (LPed-2 and LPed-3) of the left pedal ganglion of Planorbarius corneus were shown to have two kinds of cholinoreceptors (ChR) on their membrane. One kind of ChR is a classical nicotinic receptor which is sensitive to nicotinomimetics and can be blocked by tubocurarine; the depolarization caused by activation of this ChR type is chloride-dependent. The other kind of ChR, which mediates a potassium-dependent hyperpolarization, has some common features with muscarinic (M) ChR of vertebrates, being sensitive to the muscarinomimetics, dioxolane F-2268, methylfurmethide, mecholyl, and arecoline, although insensitive to oxotremorine. The sensitivity of this receptor to muscarine, itself, was not tested. Like the muscarinic ChR of vertebrates, it can be blocked by benzilylcholine mustard, but, in contrast to vertebrate muscarinic receptors, it cannot be blocked by atropine and cannot distinguish between the optical isomers of F-2268. TEA, mytolon, and cooling prevent the hyperpolarization caused by ACh and muscarinomimetics. The two kinds of ChR in P. corneus neurones seem to be similar to those found by Kehoe24-26 on the medial cells of Aplysia pleural ganglia, both in their pharmacological characteristics and in the ionic permeability changes which they control.

[Comparative findings on the stereoselectivity of cholinoreceptors]. / Sravnitel'nye dannye o stereoselektivnosti kholinoretseptorov

The potency of the optical isomers of the muscarinomimetic agent 2-methyl-4-dimethylaminomethyl-1.3-dioxolane methiodide (F-2268) was compared on cholinoreceptors, (ChR) of different animals. The greatest difference between optical isomers was observed on the muscarinic ChR of guinea pig ileum smooth muscle cis-L(+)isomer being more than hundred times as potent as cis-D(-)isomer. On the ChR of muscarinic type in the holothuria Cucumaria japonica retractor muscle, cis-L(+)isomer was 25 times as efficient as cis-D(-)isomer. On the ChR of sea urchin and sipunculid locomotor muscles, optical isomers differ only 3 to 5 times. There was no difference between the effect of optical isomers on the ChR of muscarinic type which mediate hyperpolarization in the neurones of the gastropod mollusc Planorbarius corneus. This suggest that some changes in ChR stereoselectivity may occur in the course of evolution.

[Study of the cholinoreceptive membrane of an isolated identified neuron of the mollusk Planorbarius corneus]. / Izuchenie kholinoretseptivnoi membrany izolirovannogo identsifitsirovannogo neirona molliuska Planorbarius corneus

An identified neuron (L Ped-2) of the Planorbarius corneus left pedal ganglion was isolated after the treatment of the ganglionic ring with pronase. The LPed-2 retains after the isolation the main features characteristic of this neuron in the ganglion. Nicotinomimetics (nicotine, suberyldicholine) produced depolarization whereas muscarinomimetics (F-2268, arecoline, methylfurmethide, acetyl-beta-methylcholine) hyperpolarized the cell membrane. Acetylcholine (ACh) in small concentrations (less than 1.10(-6) M) caused depolarization followed by hyperpolarization; greater concentrations depolarized the cell membrane. In the presence of tubocurarine ACh produced pure hyperpolarization. The conclusion was drawn that two kinds of cholinoreceptors exist on the membrane of LPed-2 neuron which differ both in pharmacological properties and in the sign of the response they mediate. The isolated neuron is much more sensitive to cholinomimetics than the same neuron in the ganglion.

[Hyperpolarization response of an identified neuron of Planobarius corneus mollusks to several cholinomimetic substances]. / Giperpoliarizatsionnyi otvet identifitsirovannogo neirona molliuska Planorbarius corneus na nekotorye kholinomimeticheskie veshchestva

Two kinds of responses to cholinomimetics were found on the identified neuron (P-2) of Planorbarius corneus pedal ganglion using microelectrode technique. Nicotinomimetics caused depolization whereas some muscarinomimetics caused hyperpolarization of the neuron membrane. Acetylcholine usually depolarized the neuron membrane but after the blockade of nicotinic receptors with tubocurarine one can reveal a hyperpolarizing action of acetylcholine. These findings suggest that two kinds of receptors exist on the P-2 neuron membrane and these receptors differ both in pharmacological characteristics and in ionic permeability changes they control.