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Biomedical subjects

O A Krishtal

Publications and source records attributed to O A Krishtal.

At least 55 records · Page 3Linked to original sources
PubMed1986

Are sulfhydryl groups essential for function of the glutamate-operated receptor-ionophore complex?

We monitored glutamate- or kainic acid-induced inward currents in pyramidal neurons of the rat hippocampus to determine a possible chemical modification of sulfhydryl residues on glutamate-receptor-ionophore complexes. Organic and inorganic mercury compounds such as HgCl2 and n-chloromercuribenzoate, 5,5'-dithiobis (2-nitrobenzoic acid) and N-ethylmaleimide depressed glutamate- or kainate-induced responses while the mercury compounds inhibited the kainate response, in a non-competitive manner. The responses inhibited by these agents were dose-dependently recovered by adding cysteine or glutathione. These observations suggest that the excitatory glutamate-receptor-ionophore complex includes sulfhydryl residues, components which may play a role in related functions.

Animals↗
PubMed1986

Excitatory amino acid receptors in hippocampal neurons: kainate fails to desensitize them.

The excitatory responses to L-glutamate (L-Glu), quisqualate (QA) and kainate (KA) have been investigated in isolated pyramidal cells from rat hippocampus using intracellular perfusion and concentration clamp techniques. The responses to L-Glu and QA demonstrated rapid desensitization and complete cross-desensitization, while KA produced a non-desensitizing response. The activation of KA response was determined by the level of desensitization induced by L-Glu or QA pretreatment. It is concluded that QA, KA and L-Glu activate the same excitatory receptors with apparent Kd values of 9.3 X 10(-5) M, 5.0 X 10(-4) M and 1.1 X 10(-3) M, respectively.

Animals↗
PubMed1986

'Concentration-clamp' study of gamma-aminobutyric-acid-induced chloride current kinetics in frog sensory neurones.

Kinetics of the activation and desensitization phases of gamma-aminobutyric acid (GABA)-induced Cl- current (ICl) were studied in single frog sensory neurones using the 'concentration-clamp' technique which enables perfusion of drugs with the time constant of about 3 ms. Both activation and desensitization phases of GABA response consisted of a single exponential at low concentrations and a double exponential at high concentrations. The time constant of the fast kinetic component in each phase was relatively stable, about 5 ms for activation and 3 s for desensitization over concentrations from 3 X 10(-5) to 3 X 10(-4) M, whereas those of the slow kinetic component decreased with increasing concentrations. The two kinetic components in both phases showed the same reversal potential. The slow and fast activation components recovered sensitivity from desensitization with different time courses: the recovery rate of the fast activation component was slow and that of the slow one, rapid. The peak ICl elicited at GABA concentrations below 10(-5) M increased disproportionally at more negative membrane potentials, thereby suggesting that the activation kinetics is voltage dependent. The steady-state ICl-voltage relationship obtained with less than 10(-5) M-GABA showed a non-linearity, probably due to voltage dependence of activation rather than that of desensitization kinetics. These results suggest the presence of at least two different GABA receptor-Cl- ionophore complexes with a different affinity and kinetics.

Action Potentials↗
PubMed1983

Receptor for ATP in the membrane of mammalian sensory neurones.

ATP-activated conductance has been found in a large number of neurones isolated from various sensory ganglia of the rat and cat. The inward current produced by ATP (Kd = 5 x 10(-6) M) is carried by cations and demonstrates rapid activation and slow desensitization. The sequence of agonists (ATP greater than ADP with AMP and adenosine ineffective) is different from those previously described for purinergic receptors P1 and P2.

Adenosine Triphosphate↗
PubMed1981

A "receptor" for protons in small neurons of trigeminal ganglia: possible role in nociception.

Neurons of the rat's trigeminal ganglion were enzymatically isolated and investigated under the conditions of intracellular perfusion and voltage clamp. Recently discovered proton-activated sodium conductance was found in about half of the neurons. The majority of these proton-sensitive neurons (74%) were less than 26 micrometer in diameter, whereas most of the proton-insensitive cells (75%) were larger than 26 micrometer in diameter. The possibility is discussed that the small proton-sensitive neurons may participate in nociception.

Animals↗
PubMed1981

Receptor for protons in the membrane of sensory neurons.

The neurons isolated from spinal ganglia and from the ganglion of trigeminal nerve of a rat were investigated in the conditions of intracellular perfusion and voltage clamp. Many cells responded to rapid changes of the external pH from 7.4 to l.9 and lower values by pH-dependent desensitizing inward current. This current was saturated at pH 5.4 (pKa 6.2) and carried by Na+ and K+ ions )PK:PNa approximately equal to 0.1). The discovered mechanism is capable of producing depolarization of the neuronal membrane in response to a weak acidification of the external medium.

Animals↗
PubMed1981

Calcium inward current and related charge movements in the membrane of snail neurones.

1. Isolated and intracellularly perfused neurones from the snail Helix pomatia have been investigated under voltage-clamp conditions. Calcium inward current and asymmetric displacement current were examined. 2. Two components of the asymmetric displacement current have been distinguished. One of them was irreversibly blocked by intracellular fluoride together with the calcium inward current. Another component (about 20%) was not affected. The relation of the fluoride-sensitive asymmetric displacement current to the activity of calcium channels was investigated. 3. The amounts of charge displaced by the on- and off-responses of the asymmetric current were similar. The maximum charge displacement was between 1500 and 2000 electron charges/micrometers 2. 4. The normalized steady-state voltage distribution curve of the displaced charge coincided with the square root of the normalized calcium conductance. The slope was 4 mV per e-fold change for the calcium conductance and 8 mV for te charge distribution. Thus, the effective valencies were close to 6 (for the calcium conductance) and 3 (for the charge distribution), suggesting two gating particles per calcium channel. 5. The on-process of the calcium inward current fitted m2 kinetics. The time constant tau m corresponded to the time constant tau ason of the asymmetric current in a wide range of tested voltages. This correspondence failed only at small depolarizations where tau m exceeded tau ason. 6. The 'off' time constants of the calcium inward current (tau Caoff) and the asymmetric current (tau asoff) examined at -40 mV did not depend significantly on the test pulse height. The ratio tau asoff/tau Caoff varied between 1.7 and 2.5. 7. Calcium inward-current relaxation kinetics were measured for small shifts of membrane potential (Vtest = -2 mV) applied at the peaks of the current. The time constants were smaller than tau m and depended only weakly on voltage. 8. It is concluded that the fluoride-sensitive asymmetric displacement current is related to the activation of calcium channels.

Animals↗
PubMed1981

Conductance of the calcium channel in the membrane of snail neurones.

1. Isolated neurones from the snail Helix pomatia were investigated under voltage clamp at 21-23 degrees C. The cells were internally dialysed and the current through small electrically isolated patches of the membrane was measured. The area of the patches was 30-500 micrometers 2 (1/1000-1/100 of the cell surface). The internal resistance of the membrane patches was 10(9)-10(10) omega. 2. In order to obtain the maximum conductance of the calcium channels an external solution containing 130 mM-Ba2+ or Ca2+ and an internal solution containing Tris glutamate and 5 mM-EGTA were used. Fluctuations due to the activity of calcium channels have been detected and analysed. 3. The power density spectra of barium current fluctuations were calculated for conductance values from 3% to 30% of the maximum conductance in the frequency band 1-1000 Hz. They were fitted to a spectral density function of the Lorentz form. The half-power frequency of the spectra was 227 +/- Hz (S.E.). It did not reveal any distinct voltage dependence. 4. The current flowing through a single calcium channel was calculated from the variance-to-mean relationship. Its value for the transfer of Ba2+ ions is iBa = 0.20 +/- 0.02 pA (S.E.). Single channel current was not affected by the membrane potential (since the equilibrium potential was high) nor by inactivation. The maximum calcium inward current which flows through a single calcium channel is about 0.1 pA and corresponds to a conductance gamma Ca = 0.5 pS (calculated for an equilibrium potential of 200 mV). This estimate gives an upper limit to gamma Ca. 5. The parameters of calcium channels modified by external EGTA have been evaluated. Measurements were performed in an external solution containing 200 mM-Na+. The current carried by a single modified calcium channel is iNa = 1.0 +/- 0.2 pA (S.E.) (gamma Na approximately 8.0 pS).

Animals↗
PubMed1977

Separation of sodium and calcium currents in the somatic membrane of mollusc neurones.

1. Characteristics of the transmembrane ionic currents under controlled changes in ionic composition of extra- and intracellular medium were studied in isolated neurones from the ganglia of molluscs, Helix pomatia, Limnea stagnalis and Planorbis corneus. The neurones were investigated by a new technique which allows for dialysis of their interior and for clamping of the potential at the surface membrane without using micro-electrodes.2. Replacement of K ions by Tris inside the neurones eliminated the outward K current so that the actual time course of the inward current could be measured. The latter was separated into two additive components, one of which was carried by Na ions and the other one by Ca ions.3. Both inward currents were unaltered by tetrodotoxin (TTX); however, Ca current could be separately blocked by externally applied Cd ions (K(d) = 7.2 x 10(-5)M) and by the use of fluoride as an intracellular anion.4. No reversal of Na inward current could be achieved in neurones dialysed with Na-free solution, indicating the absence of outward current carrying ions through the corresponding channels. With 5 mM-Na inside the cell, the equilibrium potential was close to the value predicted by the Nernst equilibrium.5. A non-specific outward current could be detected in K-free cells at membrane potentials exceeding 20-40 mV. Its time course was proportional to 1 - exp (-t/tau(ns)). Cd ions depressed this current. The presence of the non-specific outward current made an exact measurement of the equilibrium potential for the Ca inward current impossible.6. The kinetics of Na inward currents could be described by m(3)h and those of the Ca current by m(2)h law. The corresponding values for V(m) = 0 are: tau(m)(Na) = 1.1 +/- 0.5 msec, tau(m)(Ca) = 2.4 +/- 1.0 msec, tau(h)(Na) = 7.9 +/- 2.0 msec. The inactivation of Ca current included two first-order kinetic processes with tau(h1) = 50 +/- 10 msec and tau(h) = 320 +/- 30 msec.7. The data presented are considered to be a proof of the existence of separate systems of Na and Ca ion-conducting channels in the nerve cell membrane.

Animals↗
PubMed1977

Effects of calcium and calcium-chelating agents on the inward and outward current in the membrane of mollusc neurones.

1. Effects of internal and external Ca and Ca-chelating agents, EGTA and EDTA on transmembrane ionic currents were studied in isolated, internally dialysed neurones from the molluscs, Helix pomatia and Limnea stagnalis.2. The possible pharmacological effect of internally applied EGTA was investigated on the background of constant free Ca concentration (5.3 x 10(-9)M). EGTA had no effect on Ca and Na inward currents but considerably depressed the delayed K outward current. No effective removal of this action could be achieved by the elevation of intracellular free Ca.3. In the absence of divalent cations in the external medium, EGTA (as well as EDTA) applied either intra- or extracellularly caused the appearance of a very large Na inward current with kinetics similar to those of Ca inward current and with the reversal potential around 10 mV. Effective concentrations of chelating agents were 0.1 mM (extracellular) and 1.0 mM (intracellular).4. Increase in intracellular Ca in the absence of EGTA (by dialysis of the cell with Ca-saturated solutions) did not produce any significant effect on the delayed K outward current. The small change observed in this current could be evaluated as a depression of maximum slope conductance and a shift to more negative membrane potential.5. Ca inward current has been found extremely sensitive to internal Ca. 5.8 x 10(-8)M of internal free Ca produced its complete depression. This effect was reversible. Na inward current could be inhibited with 3.5 x 10(-7)M intracellular Ca.

Animals↗