[Kinetics of work of ion channels operated by nicotinic cholinoreceptors in the membrane of mollusk neurons]. / Kinetika raboty ionnykh kanalov upravliaemykh nikotinovymi kholinoretseptorami v membrane neironov molliuska.

The patch-clamp technique in cell-attached configuration was applied to investigate suberyldicholine-induced currents in Planorbarius corneus neurons. The single channels currents registered as inward ones at hyperpolarization of the patches were due to chloride ions efflux from the cell. Suberyldicholine (5 mumol/l) was added into the patch electrode. Usually there were more than one channel in the membrane fragment under the clamp control. The open and closed times, bursts and clusters' lengths were measured and histograms of single-channel parameters were obtained. Histograms were approximated by a sum of exponentials. Single exponentials were fitted to open times; to = 27 +/- 3 ms (n = 21). Histograms of closed times were fitted by three exponentials: tc1 = 9.5 +/- 1.0 ms (n = 21)--short gaps; tc2 = 171 +/- 33 ms (n = 19)--intermediate gaps: tc3 = 5.2 +/- 1.0 s (n = 21)--long gaps. The openings were grouped in bursts: tb2 = 203 +/- 23 ms (n = 10) and in clusters of bursts: tk3 = 1.5 +/- 0.5 s (n = 9). There were some evidences that the single burst was the result of opening, closing and reopening of just the same channel. A kinetic model with one open and three nonconducting states is plausible for single-channel data. Two long-lasting closed times may be associated with desensitization states of the receptor-channel complex. Estimates of the kinetic model parameters were obtained, that may be useful in the further study of a mode of action for cholinergic drugs in Planorbarius corneus neurons.

[Chlorine channels activated by suberyldicholine in mollusk neurons]. / Khlornye kanaly, aktiviruemye suberildikholinom v neironakh molliuska.

Patch-clamp technique in cell-attached configuration was applied to investigate ion permeability induced by suberyldicholine in the neurons of freshwater mollusc Planorbarius corneus. The inward currents through single channels were registered at patch potentials 50-100 mV more negative than resting potential of the cell. When the patch pipette contained suberyldicholine (5 mol/l), single channel currents were recorded which grouped in bursts and bursts of openings could themselves be grouped together in clusters of bursts. The desensitisation was not too pronounced: usually we were able to observe single-channel currents for 20-30 minutes. The unit conductance gamma was found to be about 10 pS.

[Changes in the neuronal membrane potential of the mollusk Planorbarius corneus under the action of cardiac glycosides]. / Izmenenie membrannogo potentsiala neironov molliuska Planorbarius corneus pri deistvii serdechnykh glikozidov.

In experiments on isolated neurones from the gastropod mollusc P. corneus, strophantin and digoxin in low concentrations produce slow hyperpolarization, in higher ones--depolarization; at concentrations about 1 mM, hyperpolarization was more evident. In all cases, the decrease in membrane resistance was observed. Presumably, membrane permeability for potassium ions increases. During application of the drugs in concentrations 10-100 microM, hyperpolarization may be masked by depolarization due to block of Na,K-pump. Higher concentrations, increasing potassium permeability of the membrane, may result in substitution of depolarization by hyperpolarization.

[A single calcium channel with anomalous rectification in mollusk neurons]. / Odinochnyi kalievyi kanal s anomal'nym vypriamlenium v neironakh molliuska.

The patch clamp technique was used to examine the properties of an inward-rectifying potassium channel in the cell membrane of freshwater mollusc Planorbarius corneus neurons. Inward currents of single channels were observed at potentials more negative than potassium equilibrium potential (EK), when microelectrode contained potassium ions (50 mmol/l) and potassium channel blockers: tetraethylammonium, barium or cesium ions (10-20 mmol/l). The conductance of the single channel was equal to 81 +/- 12 pS at 50 mmol/l potassium ion concentration in the patch electrode. At potentials more positive than EK the conductance sharply decreased to 0 pS. The times of the open state of the closed one of the channel and probability of the open state existing for the ionic channel were estimated with various constant potentials. It was revealed that the channel openings were grouped in bursts. The lifetime of the open state and burst duration decreased with hypopolarization of the patch.

[Blocking effect of furosemide on the chloride permeability of mollusk neuron membranes induced by acetylcholine and gamma-aminobutyric acid]. / Blokiruiushchee deistvie furosemida na khlornuiu provodimost' membrany neironov molliuska, indutsiruemuiu atsetilkholinom i gamma-aminomaslianoi kisloty.

Furosemide (2.10(-4) to 1.10(-3) g/ml) was shown to prevent the increase of chloride conductance induced in isolated neurons of freshwater mollusc Planorbarius corneus by ionophoretic application of acetylcholine, suberyldicholine or gamma-aminobutyric acid. Furosemide caused no shift in the reversal potential of the chloride-dependent responses if the experiments were carried out employing microelectrode filled with potassium sulphate. When potassium chloride-filled microelectrodes were used, the reversal potential became less negative in the presence of furosemide. This effect seems to be due to the blocking of the active transport of chloride by furosemide. Neither sodium-dependent, nor potassium-dependent responses induced by cholinoreceptor activation were influenced by furosemide. Furosemide was found to diminish both the amplitude and the rate of chloride-dependent responses. The lack of selectivity with respect to acetylcholine or gamma-aminobutyric acid suggests that furosemide blocks the chloride channels of chemoceptive membrane which are probably common to acetylcholine and gamma-aminobutyric acid and does not affect their receptors.

[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.

[Study of the chemoreceptor membrane of identified neurons of the gastropod mollusk Planorbarius corneus with different technics of applying chemicals]. / Issledovanie khemoretseptivnoi membrany identifitsirovannykh neironov briukhonogogo molliuska Planorbarius corneus pri raznykh sposobakh applikatsii veshchestv.

Changes in the membrane potential caused by acetylcholine or gamma-aminobutyric acid when added to the perfusion fluid were compared with those induced by their local application to the neuron soma membrane from the micropipette (diameter 100-300 mu). With equal drug concentrations, the responses were found to be of similar amplitude with either method of application. The rate of changes in the membrane potential proved to be however several times higher in the case of local application. Using voltage--clamp technique and local drug application, the dose-response relationships were studied during selective activation either of two kinds of cholinoreceptors available on the identified neuron membrane. The saturation of the muscarinic receptors was shown to be attained at smaller agonist concentrations, the absolute value of maximal response being at least one order of magnitude lower than in case of nicotinic cholinoreceptors of the same cell.

[A direct microfluorimetric study of organic acid passage through the proximal tubule cells of the surviving Rana temporaria frog kidney]. / Priamoe mikrofluorimetricheskoe izuchenie prokhozhdeniia organicheskoi kisloty cherez kletki proksimal'nykh kanal'tsev perezhivaiuschei pochki liagushki Rana temporaria

Accumulation of acid fluorochrome in proximal tubuli in the frog surviving kidney has been investigated. Mean concentration of fluorochrome in the tubuli is linearly related to the duration of incubation. Changes in the mean rate of transport of fluorochrome into the tubuli induced by changes in its external concentration are satisfactorily described by Michaelis-Menten equation, Michaelis constant being equal to 2.1-10(-4). Some equations are suggested which describe the kinetics of organic acid transport across basal and apical membranes of cells.