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Biomedical subjects

V I Pidoplichko

Publications and source records attributed to V I Pidoplichko.

At least 37 records · Page 2Linked to original sources
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

[Transmembrane ionic currents in neuroblastoma cells].

Isolated neuroblastoma cells (clone A-1 from clone N-18) were investigated by means of the intracellular dialysis technique. Changes in the ionic composition of intra- and extracellular media show that the fast inward current is carried by Na ions and delayed outward current is carried by K ions. Na inward current was blocked by TTX. Calcium inward current was not observed. Substitution of Na ions for K ions showed that PNa: PK = 7:1. A relatively low potassium conductance was found in the neuroblastoma cells.

Action Potentials↗
PubMed1977

[Separation of ionic currents responsible for action potential generation in isolated neurons of frog spinal ganglia].

The technique was developed for isolating neurons from the frog spinal ganglia. The isolated cells completely preserved electrical excitability and were investigated under intracellular dialysis conditions. Fast and slow inward current components were found. They were separated by TTX and cadmium: the fast inward current component was blocked by TTX, while the slow inward current was blocked by cadmium. Slow inward current diminished in Na-free solution and calcium ions are supposed to participate in its transfer.

Action Potentials↗
PubMed1977

[Analysis of current fluctuations shunted from small portions of the membrane of a nerve cell soma].

A method was developed to allow the registration of ionic current through the small areas of the membrane (10 mu2). The aim of the method is to obtain information on the properties of single ionic channels by the fluctuation analysis. The current through single Ca channel while transferring Ba (130 mM in the external media) is 0.21 +/- 0.06 X 10(-12) A according to tentative estimation. The corresponding value for Ca transfer is 0.1 X 10(-12) A. The upper limit for the single Ca channel conductance value is gCa less than or equal to 0.6 X 10(-12) PHI-1.

Animals↗