Local changes of resistance in the retinal horizontal cell evoked by changes in membrane potential

A steady current (10·10^–10–6·10^–9 A) was passed by means of a bridge circuit through a recording microelectrode inserted into a horizontal cell of the turtle retina. Illumination of the retina caused an increase in the resistance of the microelectrode circuit (by 10–80 M), causing a change in the shape of the recorded response of the horizontal cell to light. The change in resistance was shown to take place, not on the cell membrane itself, but inside the cell close to the microelectrode tip. The effect described can be reproduced by passing a current through one barrel of a double-barreled microelectrode alongside the recording barrel, but the strength required for this current was greater than that passed through the recording barrel. If the membrane potential of the horizontal cell was made equal to the equilibrium potential (by means of a steady current passed through extracellular electrodes) the hyperpolarization response to light and the effect of the increase in resistance of the microelectrode circuit disappeared simultaneously. On the other hand, artificial hyperpolarization of the cell membrane caused an increase, but depolarization caused a decrease in the resistance of the microelectrode circuit. It is postulated that the observed effect is due to blocking of the microelectrode tip by an intracellular structure whose resistance varies with a change in membrane potential.Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol.5, No.4, pp.432–441, July–August, 1973.     

Investigation of the nature of electrical responses of horizontal cells of the fish retina

On the basis of the syncytial structure of the layer of horizontal cells of the fish retina, a method is developed which effectively shifts the membrane potential of cells by means of an electrical current. It is shown that the response of L-type horizontal cells to light and electrical stimulation of the retina is reversed when the membrane of the horizontal cells is depolarized by a direct current. The equilibrium potential of the cells was near the zero level. Consequently, the depolarization response of the horizontal cells to disconnection of the light and to electrical stimulation of the retina is an excitatory postsynaptic potential, whereas hyperpolarization of the horizontal cells to light is a decrease of this potential. It is shown that the membrane of fish horizontal cells have pronounced nonlinear properties: in the case of strong depolarization and especially in the case of hyperpolarization its impedance drops markedly. The latter probably occurs due to an increase of the permeability of the nonsynaptic membrane of the horizintal cells for K⁺. This can also explain the decrease of membrane impedance during the hyperpolarization response of the horizontal cells to bright light. The available data indicate the presence of regenerative properties of the membrane of horizontal cells.Institute of Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 89–98, January–February, 1971.     

Effect of polarization of horizontal cells of the pike retina on spread of their electrical potentials

The spread of electrical responses over the layer of horizontal cells of the pike retina was investigated at different levels of their membrane potential varied by application of a steady current. Depolarization of the membrane, accompanied by an increase in its resistance, led to an increase in its time constant and length constant, so that electrical waves spread further over the layer of horizontal cells. The effect of polarization was thus due to the nonlinear membrane properties of the horizontal cells, i.e., to the increase in their resistance on depolarization and its decrease on hyperpolarization. In some cases this nonlinearlity was manifested as a special type of regeneration: the same strength of steady current crossing the membrane of the horizontal cells corresponded to two stable levels of the membrane potential. The role of various factors (changes in resistance of the extrasynaptic and subsynaptic membranes of the horizontal cells, the presynaptic effect of the current) determining the spread of the potentials over the horizontal cells under natural conditions during photic stimulation is discussed.Institute of Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 1, pp- 90–96, January–February, 1972.     

Light-Induced Changes in Photoreceptor Membrane Resistance and Potential in Gecko Retinas : II. Preparations with Active Lateral Interactions

The time-course of light-induced changes in membrane voltage and resistance were measured in single photoreceptors in eyecup preparations of Gekko gekko. A small circular stimulus directed toward the impaled receptor produced membrane hyperpolarization. Application of a steady annular light to the receptor periphery resulted in diminution of the receptor's response to the stimulus. The effects of illumination of the surrounding receptors were isolated by directing a small, steady desensitizing light to the impaled receptor and then applying a peripheral stimulus. Brief stimuli produced a transient decrease in resistance with rapid onset and offset, a time-course similar to that of the response diminution. For some cells a depolarization that coincided with the resistance decrease was seen. During illumination with prolonged stimuli the resistance decrease was followed by a slow increase. After offset resistance rose transiently above the original value and then returned slowly to its original value. The slow resistance changes were not accompanied by changes in membrane voltage. The response diminution, resistance decrease, and depolarization were not observed in retinas treated with aspartate or hypoxia. It is therefore concluded that these effects are mediated by horizontal cells. The diminution is achieved by shunting the receptor potential and may play a role in field adaptation.     

Peculiarities of synaptic transmission between photoreceptors and horizontal cells

A previously advanced hypothesis, according to which the transmitter which depolarizes the membrane of horizontal cells is continually liberated in the dark, and ceases to be liberated in the light, is tested experimentally. The data presented show that a current acting on presynatic receptor endings evokes a depolarizing response in horizontal cells to short current impulses passing through the retina (anode on receptor surface, cathode in vitreous body). These receptor endings are depolarized, which evidently leads to liberation of the transmitter from the receptors. Experiments with electrical stimulation of the retina have shown that treatment of the retina with potassium cyanide disrupts synaptic transmission between the receptor and horizontal cell. A potential equal to their membrane potential is established in horizontal cells in bright light; this potential is evidently the true rest potential of these cells. The relative stability of the membrane potential of horizontal cells in light with change in temperature is evidence in support of this assumption. In the dark, the membrane potential increases considerably with increase in temperature; this effect is possibly due to a rise in the rate of decomposition of the depolarizing transmitter. Evidence in support of this hypothesis is the rise in steepness of the falling phase of the response of the horizontal cells to electrical stimulation observed on elevation of the temperature.Institute for Problems of Information Transmission of the Academy of Sciences of the USSR, and Institute of Higher Nervous Activity and Neurophysiology of the Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 79–86, January–February, 1970.     

Nonsynaptic membrane of retinal horizontal cells as a slow potential amplifier

A simplified model of the membrane of horizontal cells of the L-type is designed to reflect two principal features of these cells previously studied experimentally: 1) their hyperpolarization response to light is the result of a decrease in the EPSP that is kept constant in darkness; 2) the resistance of their nonsynaptic membrane is reduced during hyperpolarization within physiological limits (from 0 to−70 mV). The model also reproduces properties of the horizontal cells such as the low membrane potential in darkness, reversal of the response to light during depolarization beyond the zero level, mutual amplification of color signals, saturation of the response to bright light, steady-state volt-ampere characteristics in darkness and light, and the amplitude characteristic curve which often has a steep part within a certain range of membrane potentials. The presence of hysteresis loops of the volt-ampere and amplitude characteristic curves of the horizontal cells predicted by the model was confirmed experimentally on the fish retina. Analysis of the model and results obtained with it show that the nonsynaptic membrane of the horizontal cells can actively amplify slow graded potentials.     

Model feedback mechanism between horizontal cells and photoreceptors of the vertebrate retina

A model with nonlinearity of the photoreceptor presynaptic membrane as its important distinguishing feature was created on the basis of the hypothesis that feedback between the horizontal cells and photoreceptors is effected by a current generated by the subsynaptic membrane of the horizontal cells and leaking partly into the photoreceptors. Measurements with the model also reproduced experimental observations such as depolarization of the cone during hyperpolarization of the horizontal cell in response to the showing of a ring of light or passage of an electric current, and also certain special features of the current-voltage curves of the cones.Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 1, pp. 86–94, January–February, 1977.     

Ionic mechanisms of nonlinearity of the retinal horizontal cell membrane

Changes in ionic conductance lying at the basis of nonlinearity of the current-voltage characteristic curve of the cell (nonsynaptic) membrane of horizontal cells were studied in experiments on the goldfish and turtle retina. All measurements were made during blocking of synaptic transmission by bright light or Co⁺⁺. An increase in the K⁺ concentration led to depolarization and to a reduction of the steepness of the hyperpolarization branch of the current-voltage curve, whereas a decrease in K⁺ had the opposite effect. Changes in the Cl^– or Na⁺ concentrations had no significant effect on membrane potential or on the shape of the current-voltage curve. The principal potential-forming ion in the horizontal cells is thus K⁺; conductance for Cl^– is absent or very low, and conductance for Na⁺ also is evidently small. In the presence of Ba⁺⁺ (2–5 mM) the steepness of the hyperpolarization branch of the current-voltage curve was increased and the whole curve became more linear. It is concluded that nonlinearity of the current-voltage curve of the horizontal cell membrane is due mainly to potential-dependent potassium channels, whose conductance increases during hyperpolarization; this increase in conductance is blocked by Ba⁺⁺. An increase in the Ca⁺⁺ concentration to 20 mM led to an increase in steepness of the depolarization branch of the current-voltage curve, suggesting that depolarization increases membrane conductance for Ca⁺⁺.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 5, pp. 531–539, September–October, 1981.     

Voltage-dependence of cobalt-induced blockade of synaptic transmission between photoreceptors and horizontal retinal cells

Synaptic transmission between photoreceptors and horizontal cells in the turtle retina blocked by Co²⁺ ions can be restored by passing constant radial current through the retina which depolarizes presynaptic receptor terminals. This finding is unassociated with current action on horizontal cells themselves, since polarization of these cells via an intracellular microelectrode did not restore response to light. The unblocking effect of depolarization at the receptor synaptic endings consists of two components: the opening of additional calcium channels not blocked by Co²⁺ at the presynaptic membrane and cobalt-induced voltage-dependent blockade of clacium channels. The latter may explain the paradoxical phenomenon of increased response to the action of moderate light in horizontal cells during cobalt-induced partial blockade of synaptic transmission.Institute for Research into Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 20, No. 3, pp. 374–383, May–June, 1988.     

Membrane currents in retinal bipolar cells of the axolotl

By whole-cell patch-clamping bipolar cells isolated from enzymatically dissociated retinae, we have studied the nonsynaptic ionic currents that may play a role in shaping the bipolar cell light response and in determining the level of voltage noise in these cells. Between -30 and -70 mV, the membrane current of isolated bipolar cells is time independent, and the input resistance is 1-2 G omega. Depolarization past -30 mV activates an outward current (in less than 100 ms), which then inactivates slowly (approximately 1 s). Inactivation of this current is removed by hyperpolarization over the range -20 to -80 mV. This current is carried largely by K ions. It is not activated by internal Ca2+. The membrane current of isolated bipolar cells is noisy, and the variance of this noise has a minimum between -40 and -60 mV. At its minimum, the standard deviation of the voltage noise produced by nonsynaptic membrane currents is at least 100 microV. The membrane currents of depolarizing bipolar cells in slices of retina were investigated by whole-cell patch-clamping. Their membrane properties were similar to those of isolated bipolar cells, but with a larger membrane capacitance and a smaller input resistance. Their membrane current noise also showed a minimum near -40 to -60 mV. The time-dependent potassium current in axolotl bipolar cells is not significantly activated in the physiological potential range and can therefore play little role in shaping the bipolar cells' voltage response to light. Differences in the waveform of the light response of bipolar cells and photoreceptors must be ascribed to shaping by the synapses between these cells. The noise minimum in the bipolar membrane current is near the dark potential of these cells, and this may be advantageous for the detection of weak signals by the bipolar cells.     

Investigation of electrophysiological responses of Neurospora crassa to blue light

The influence of light in a spectrum range of 350–500 nm 20 W m^-2 (20,000 erg · cm^-2 · s^-1) has been studied in the mycelial cells of Neurospora crassa. Light-induced input resistance and membrane potential changes can be measured by means of intracellular microelectrodes. The value of the input resistance reached maximum after a 2–5 min illumination. The maximum hyperpolarization of the cell membrane reaching 30–40 mV was observed after 20–25 min illumination, when the input resistance values did not differ significantly in the illuminated and non-illuminated cells.     

Membrane potential clamping in horizontal cells of the fish retina

The membrane potential of horizontal cells of the retina was clamped by uniform polarization of the layer of these cells by a current passed through extracellular electrodes. The volt-ampere characteristic curve of the synaptic membrane of the horizontal cells in some cases had segments with negative slope. With a sharp change in the level of voltage clamping the time taken for the resistance of the membrane to change was under 20 msec. Comparison of responses to photic stimulation recorded with and without voltage clamping showed that participation of the nonsynaptic membrane in the generation of responses to photic stimulation can affect their shape substantially.Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 4, pp. 402–407, July–August, 1977.     

Effects of conditioning polarization on the membrane ionic currents in rat myometrium

Summary Membrane ionic currents were measured in pregnant rat uterine smooth muscle under voltage clamp conditions by utilizing the double sucrose gap method, and the effects of conditioning pre-pulses on these currents were investigated. With depolarizing pulses, the early inward current was followed by a late outward current. Cobalt (1mm) abolished the inward current and did not affect the late outward currentper se, but produced changes in the current pattern, suggesting that the inward current overlaps with the initial part of the late outward current. After correction for this overlap, the inward current reached its maximum at about +10 mV and its reversal potential was estimated to be +62 mV. Tetraethylammonium (TEA) suppressed the outward currents and increased the apparent inward current. The increase in the inward current by TEA thus could be due to a suppression of the outward current. The reversal potential for the outward current was estimated to be –87 mV. Conditioning depolarization and hyperpolarization both produced a decrease in the inward current. Complete depolarization block occurred at a membrane potential of –20 mV. Conditioning hyperpolarization experiments in the presence of cobalt and/or TEA revealed that the decrease in the inward current caused by conditioning hyperpolarization was a result of an increase in the outward current overlapping with the inward current. It appears that a part of the potassium channel population is inactivated at the resting membrane potential and that this inactivation is removed by hyperpolarization.     

Ion exchange in the horizontal cells of the retina

Experimental data indicate that the membrane potential of L-type horizontal cells of the retina to bright light (i.e., when synaptic inputs are completely closed) is close to the potassium equilibrium potential. From this observation the intracellular concentration of K⁺ and Na⁺ was estimated. The latter was found to be relatively high (tens of millimoles/liter), i.e., comparable with the intracellular K⁺ concentration. This result, coupled with data on closeness of the equilibrium potential of the photic response to zero, is evidence that besides sodium conductance, the potassium conductance of the subsynaptic membrane also participates in generation of the photic response by these cells. The steady-state sodium and potassium synaptic currents was shown to be relatively small and to vary only a little over the whole working range of potentials (from –72 to –16 mV), due to the nonlinear properties of the nonsynaptic cell membrane.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 3–10, January–February, 1982.     

On the role of horizontal cells in the mechanism of retinal adaptation

We recorded by intracellular means responses of horizontal cells of the turtle retina to light increase and decrease of different values against the starting adapting level. In measuring these responses, curves reflecting the dependence of membrane potential deflection on light intensity (amplitude characteristics — ACh) were plotted. It is demonstrated that the ACh of transitional processes (on- and off-peaks) is considerably steeper than ACh of the plateau of the potential, but embraces a much smaller range of light intensities (slightly more than 1 log. un.). During a change in intensity of the adapting background (up to 3 log. un.), the ACh of transitional processes shifts along the scale of light intensities in such a way that its steep part remains in the zone of adapting light. We followed the dynamics in time of ACh shift after the transition from one adapting brightness to another. The ACh of total impulse response was plotted for ganglionic cells of the turtle at different intensities of adapting light. Comparison of these curves with the ACh of horizontal cells shows that its peripheral components are responsible for adaptive shifts of ACh of the visual system and that horizontal cells play an important role in the mechanism of adaptation. It is hypothesized that adaptive ACh shifts are the consequence of positive feedback between the horizontal cells and receptors.Institute of Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 1, No. 2, pp. 210–218, September–October, 1969.     

S-Potentials in the Skate Retina : Intracellular recordings during light and dark adaptation

The S-potentials recorded intracellularly from the all-rod retina of the skate probably arise from the large horizontal cells situated directly below the layer of receptors. These cells hyperpolarize in response to light, irrespective of stimulus wavelength, and the responses in photopic as well as scotopic conditions were found to be subserved by a single photopigment with λ_max = 500 nm. The process of adaptation was studied by recording simultaneously the threshold responses and membrane potentials of S-units during both light and dark adaptation. The findings indicate that the sensitivity of S-units, whether measured upon steady background fields or in the course of dark adaptation, exhibits changes similar to those demonstrated previously for the ERG b-wave and ganglion cell discharge. However, the membrane potential level of the S-unit and its sensitivity to photic stimulation varied independently for all the adapting conditions tested. It appears, therefore, that visual adaptation in the skate retina occurs before the S-unit is reached, i.e., at the receptors themselves.     

Interaction between horizontal cells of the turtle retina

Interaction between horizontal cells of the turtle retina was studied by two microelectrodes (polarizing and recording), inserted into different cells at different distances apart. The presence of a direct electrical connection was demonstrated between the L cells of the same type (I, with large, and II, with small receptive fields). Its magnitude depends on the conditions of illumination and the level of the membrane potential, possibly because of the properties of the subsynaptic and nonsynaptic membranes of the horizontal cells. No direct electrical connection exists between L cells of different types. However, hyperpolarization of the type I cells through the microelectrode or by stimulation with a circle of light evoked depolarization in the type II cells. This indirect connection between the horizontal cells, also dependent on the conditions of illumination, can probably be explained by feedback to these cells from the photoreceptors. Polarization of L cells of both types had no effect on horizontal cells of color type.     

Ionic mechanisms underlying modulating effects of serotonin on acetylcholine-induced responses in Helix pomatia neurons

The ionic mechanisms underlying modulatory effects of serotonin on acetylcholine-response in identified and nonidentifiedHelix pomatia neurons were investigated using voltage-clamping techniques at the neuronal membrane. External application of 10^–5–10^–4 M serotonin to the membrane of neurons responding to application of acetylcholine depending on Na⁺ depolarization (D_Na response) reduced membrane conductivity during response to acetylcholine without changing reversal potential of acetylcholine-induced current. Acetylcholine (10^–6–10^–4 M) administration took place 1–3 min later. Neurons with response to acetylcholine application dependent on Cl⁺ depolarization (D_Cl response) or hyperpolarization (H_Cl response) behaved similarly. Analogous effects could be produced by external application of theophylline which, together with the latency and residual effect characteristic of serotonin action points to the participation of intracellular processes associated with the cellular cyclase system in the changes produced by serotonin in acetylcholineinduced response. Serotonin brought about a shift in reversal potential and an increase in the acetylcholine-induced current in those neurons where this response was associated with changed permeability at the membrane to certain types of ions. During two-stage acetylcholine-induced response of the D_Na-H_K type, serotonin inhibited the inward current stage. Mechanisms underlying modulatory serotonin action on acetylcholine-induced response in test neurons are discussed in the light of our findings.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 1, pp. 57–64, January–February, 1988.     

Changes in direct current input resistance in horizontal cells of fish retina during excitation

The input resistance of pike retinal horizontal cells was measured by means of coaxial electrodes under various conditions of illumination. With moderate intensities of illumination, the resistance (determined from a potential drop caused by the current passed through the microelectrode) increases, whereas at high saturating intensities it decreases, as compared with its value in darkness. Such changes in resistance of the horizontal cells explain the effects of input signals interaction in these cells, such as enhancement and complete saturation, observed earlier. Some properties of the horizontal cell response permit us to assume that the "active" cell response to polarization makes a substantial contribution to the measured resistance of these cells. Possible mechanisms of such changes in input resistance of horizontal cells are discussed.Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 2, pp. 210–216, March–April, 1971.     

Properties of the slow excitatory postsynaptic potential in mammalian sympathetic ganglion cells

Two types of slow excitatory postsynaptic potentials (EPSPs) with different properties were found in neurons of the rabbit superior cervical sympathetic ganglion. In our group of neurons slow EPSPs increased during artificial hyperpolarization and decreased during depolarization of the membrane. The input resistance of the cells fell or remained unchanged during the development of slow EPSPs. In the second group of cells slow EPSPs increased during depolarization and decreased during hyperpolarization. The reversal potential of these responses, determined by extrapolation, was –78.9±3.6 mV. Depolarization responses to activation of muscarinic cholinergic receptors by acetylcholine or carbachol developed in 53% of neurons with an increase in input resistance and had a reversal potential of –83.2±6.7 mV. It is suggested that in cells of the first group the ionic mechanism of the slow EPSPs is similar to that of the fast EPSPs, whereas in cells of the second group its main component is a decrease in the potassium conductance of the membrane.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 4, pp. 371–379, July–August, 1981.