[Argiopine, argiopinines and pseudoargiopinines--blockers of the glutamate receptors in hippocampal neurons]. / Argiopin, argiopininy i psevdoargiopininy--blokatory glutamatnykh retseptorov v neironakh gippokampa.

Several homologous low-molecular weight compounds were purified from venom of spider Argiope lobata. They selectively blocked ionic currents elicited by glutamate and its agonist kainate in the membrane of isolated hippocampal neurons of rat. Three groups of these compounds--argiopine, argiopinines and pseudoargiopinines, blocked glutamate- and kainate-activated ionic currents in a voltage-dependent manner, acting preferentially on agonist-activated ionic channels. These compounds did not change the Kd values for both agonists. The blocking action was partially reversible for argiopine and poorly reversible for other compounds. Rate constants for the interaction of toxins with membrane receptors were estimated from the dependences of two-component kinetics of the blocking action and its recovery on toxin concentrations. Argiopine, argiopinines and pseudoargiopinines may be useful tools for further electrophysiological and biochemical investigation of the mammalian CNS glutamate receptors.

[Blocking action of Nephila clavata spider toxin on ionic currents activated by glutamate and its agonists in isolated hippocampal neurons]. / Blokiruiushchee deistvie iada pauka Nephila clavata na ionnye toki, aktiviruemye glutamatom i ego agonistami v izolirovannykh neironakh gippokampa.

The blocking action of the Nephila clavata spider neurotoxin was studied using the concentration clamp method in isolated neurons of the rat hippocampus. Crude venom JSTX blocked L-glutamate-, quisqualate- and kainate-activated ionic currents mediated by activation of the non-N-methyl-D-aspartate (non-NMDA) membrane receptors. Ionic currents elicited by all agonists were depressed by crude JSTX venom to 34-35% of its initial amplitude with no recovery during prolonged washing. An active fraction of JSTX venom blocked ionic currents almost completely, but its action was partially reversible. The concentration dependences of blocking kinetics allowed determining the rate constants of JSTX interaction with glutamate receptors. It is supposed that JSTX blocks the non-NMDA ionic channels in some of their open states and may be one of useful tools in further biochemical and electrophysiological characterization of the glutamate-mediated synaptic transmission.

[L-glutamate-activated conductivity in the membrane of isolated pyramidal neurons of the rat hippocampus]. / L-glutamataktiviruemaia provodimost' v membrane izolirovannykh piramidnykh neironov gippokampa krysy.

Isolated pyramidal neurons from rat hippocampus were investigated under conditions of intracellular perfusion and voltage clamp using the method of rapid application of extracellular solution. It was found that the L-glutamate-activated current was carried by sodium and potassium ions with PK+/PNa+ ratio about 0.6. The dose-response relationship demonstrated one to one interaction between L-glutamate and membrane receptor with Kd value about 1.1 mmol/l.

[Comparative analysis of the characteristics of potassium channels in the membranes of spinal ganglion neurons and neuroblastoma cells]. / Sravnitel'nyi analiz kharakteristik kalievykh kanalov v membrane neironov spinal'nykh gangliev i kletok neiroblastomy.

The method of intracellular perfusion and voltage clamp was used to investigate potassium channels in the somatic membrane of the rat spinal ganglion neurons and mouse neuroblastoma cell. It is shown that potential-dependent properties of potassium channels in both types of membranes are similar while time constants of activation and inactivation are substantially higher in the neuroblastoma cells. The density of potassium channels was ten times less in the neuroblastoma cells than in the spinal ganglion neurons.

[TEA-resistant outward current in the somatic membrane of perfused nerve cells]. / Issledovanie TEA-ustoichivogo vykhodiashchego toka v somaticheskoi membrane perfuziruemykh nervnykh kletok.

The outward currents remaining after addition of 20-50 mM tetraethylammonium (TEA) to the extracellular solution were studied on perfused isolated neurons from Helix pomatia. A potassium-carried noninactivating outward current with potential-dependence and kinetics different from those of TEA-sensitive potassium currents was found. This TEA-resistant current includes a component depending on the presence of the inward calcium current. It could be abolished by replacing extracellular calcium by magnesium ions, by blocking the calcium channels with extracellular cadmium ions and their distruction by intracellular fluorid ions. An increase in the level of intracellular free carcium (by perfusing the cell with solutions containing Ca-EGTA buffer) potentiated the TEA-resistant component of the outward current and the removal of free calcium by EGTA decreased it. A conclusion is made that the somatic membrane contains outward current channels which can be activated only when calcium ions are bound to its inner surface.

[Study of the reversion potential for the slow component of the entering current in the membrane of mollusk neurons]. / Issledovanie potentsiala reversii dlia medlennogo komponenta vkhodiashchego toka v membrane neironov molliuskov.

The nature of a significant deviation of the reversal potential for the slow inward current component from calcium equilibrium potential was investigated in the snail neuron somatic membrane. It is shown that this deviation may be due to a development of a non-specific outward current during large depolarizing shifts of the clamped membrane potential. The real equilibrium potential for calcium ions in nerve cells may be of about +200 mV.

[Separation of potassium and calcium channels in the nerve cell soma membrane]. / Razdelenie kalievykh i kal'tsievykh kanalov v membrane somy nervnoi kletki.

Calcium inward and potassium outward currents were studied on internally dialysed isolated neurons of the snail Helix pomatia. Different sensitivity of the corresponding channels to changes in external pH was found. This difference was used for separation of their activation regions on the potential axis so that the characteristics of the inward and outward currents could be studied with minimal overlap. It is shown that the outward current channels possess a definite permeability to Tris ions (PTris :PK=0.05). This explains the impossibility to switch off this current by substituting Tris for internal potassium. The channels for the inward calcium current inactivate slowly with a first order kinetic; their instantaneous current-voltage characteristic reveals considerable Goldman-type rectification. The selectivity of the calcium channels to other bivallent cations is Ba:Sr:Ca:Mg=2.8:2.6:1.0:0.2.

[Effect of calcium ions on channels for entrance and exit of ionic currents in the membranes of mollusk neurons]. / Deistvie ionov kal'tsiia na kanaly vkhodiashchikh i vykhodiashchikh ionnykh tokov v membrane neironov molliuskov

A newly developed method of internal dialysis was applied together with the voltage clamp method to the isolated neurons of molluscs Helix pomatia and Limnea stagnalis. Effect of Ca on the Ca inward and K delayed outward currents was investigated. Removal of Ca from the external medium was equivalent to 25-35 mV hyperpolarization of the membrane. Internal Ca in concentrations up to 3.5-10-(7)M caused insignificant depression of K outward current. 5.7-10-(8)M of internal Ca completely blocked Ca inward current. Ca-chelating agents applied either internally or externally caused an appearance of Na inward current transferred through the Ca channels.

[Separation of the sodium and potassium channels in the surface membrane of mollusk nerve cells]. / Razdelenie natrievykh i kal'tsievykh kanalov v poverkhnostnoi membrane nervnykh kletok molliuskov

Characteristics of transmembrane ionic currents under controlled changes in ionic composition of extra-and intracellular medium were studied by means of intracellular dialysis and voltage clamp in isolated neurons from the molluscs Helix pomatia and Limnea stagnalis. The outward potassium currents were eliminated by replacement of intracellular potassium by Tris and the pure inward current could be measured. Replacement of the Ringer solution by NA-free or Ca-free solutions in the extracellular medium made it possible to separate the inward current into additive components, one of which is carried by sodium ions, and the other, by calcium ions. The sodium and calcium inward currents are shown to have different kinetics and potential dependence: taumNa = 1+/-0.5 ms, taumCa = = 3+/-1 ms, tauhNa = 8+/-2 ms, tauhCa = 115+/-10 ms when Vm = 0, GNa = 0.5 when Vm==-21+/-2 mV, GCa = 0.5 when Vm=-8+/-2 mV. Both currents were not altered by tetrodoxin (TTX), however calcium current is specifically blocked by externally applied calcium ions (2 X 10(-3) M), verapamil, D = 600 as well as by fluoride while introduced inside a cell. These data prove the existence of separate systems of sodium and calcium ion-conducting channels in the somatic membrane.