Biomedical subjects

G Waloga

Publications and source records attributed to G Waloga.

6 recordsLinked to original sources

PubMed1993

Electrical properties of Y-79 cells, a multipotent line of human retinoblastoma.

1. Whole-cell and perforated-patch tight-seal recording techniques were used to characterize the voltage-dependent membrane conductances of the Y-79 cells, a human retinoblastoma line composed of pluripotential retinal precursor cells. 2. Membrane resistance and capacitance were measured under current clamp, yielding approximate average values of 1.8 G omega and 26 pF, respectively. The cells are electrically excitable, and depolarization above -20 mV triggers slow action potentials. 3. Step depolarization of the membrane under voltage clamp elicits a high-threshold transient inward current, followed by a sustained, larger outward current. The outward current is carried by potassium ions, as determined by its susceptibility to blockage by K-channel antagonists [tetraethylammonium (TEA), Cs, and 4-aminopyridine (4-AP)] and insensitivity to reduction of external chloride concentration. 4. The isolated inward current displayed some unusual properties: its amplitude is directly related to extracellular calcium concentration, and replacement of calcium by magnesium completely abolishes it. However, none of the calcium channel antagonists tested (cadmium, nickel, nifedipine, and amiloride) exerted a substantial blockage. In addition, removal of external sodium or superfusion with tetrodotoxin significantly reduce the size of this current. 5. A single voltage-dependent conductance appears to underlie the inward current, because a variety of manipulations, such as changes in the holding potential, in the extracellular concentration of calcium or sodium, or superfusion with tetrodotoxin, failed to reveal the presence of kinetically distinct components. 6. The results suggest that a single voltage-dependent conductance mechanism underlies the depolarization-activated inward current in Y-79 cells. This channel appears to be primarily permeable to calcium, but with a significant contribution by sodium ions. Its functioning appears to be modulated by extracellular calcium.

Calcium Channel Blockers↗

PubMed1993

Induction of voltage-dependent sodium channels by in vitro differentiation of human retinoblastoma cells.

1. Neuronlike differentiation of Y-79 retinoblastoma was chemically induced in vitro, by plating the cells onto a poly-D-lysine and laminin substrate. The changes in voltage-dependent conductances after 48-72 h were examined with the whole-cell tight-seal and the perforated-patch recording techniques. 2. Although outward currents carried by potassium ions appeared qualitatively similar before and after differentiation, the depolarization-activated transient inward current displayed a pronounced acceleration of its activation and inactivation kinetics. 3. After differentiation, both the threshold of activation and the steady-state inactivation curve of the inward current are displaced in the negative direction by approximately 10-20 mV as compared with untreated cells. The current attains its peak amplitude in approximately 1 ms at maximum activating voltages, and decays within 3 ms. In contrast, in undifferentiated cells these values are on the order of 6 and 60 ms, respectively. The time to recover from inactivation is also shortened 20-fold in differentiated cells. 4. Unlike the mixed conductance of undifferentiated cells, which requires extracellular calcium, the inward current of the neuronlike differentiated cells is insensitive to manipulations of external calcium. Instead, it can be completely abolished in a reversible way by sodium removal or by micromolar concentrations of tetrodotoxin (TTX) in the bathing solution. As such, it resembles in all salient respects the voltage-dependent sodium conductance of nerve cells. 5. The fast sodium current expressed after neuronal differentiation is not the result of a progressive enhancement of an existing conductance, because no such component is discernible in undifferentiated cells. Moreover, recordings performed in cells at early stages of differentiation also failed to reveal the coexistence of the immature and the differentiated inward currents. 6. A possible account of the present observations is that the native inward current of undifferentiated Y-79 cells may correspond to a precursor form of the mature channel, and the observed developmental changes induced by chemical differentiation could be a consequence of progressive modification of the original channels, rather than expression of a separate class of proteins.

Butyrates↗

PubMed1985

Effects of inositol-1,4,5-trisphosphate injections into salamander rods.

Solitary rods were isolated by trituration of salamander (Ambystoma tigrinum) retinas. One barrel of an intracellular, double-barreled micropipette was used to record membrane voltage; the other barrel was used to pressure-inject inositol-1,4,5-trisphosphate. The injection of inositol-1,4,5 -trisphosphate induced a reversible hyperpolarization of the rod membrane. Injections of inositol-1,4,5-trisphosphate decreased the size of receptor potentials induced by dim lights. Conversely, light decreased the responses of the rod to injections of inositol-1,4,5-trisphosphate. These results suggest that inositol-1,4,5-trisphosphate might be involved in the modulation of rod membrane voltage during phototransduction.

Animals↗

PubMed1983

Effects of calcium and guanosine-3',5'-cyclic-monophosphoric acid on receptor potentials of toad rods.

Membrane potential was recorded intracellularly from rod outer segments in the isolated retina of Bufo marinus. The composition of the solution flowing over the exposed receptor side of the retina was changed rapidly and ionophoretic injections were made into single rod outer segments. Lowering the external Ca2+ concentration, adding 3-isobutyl-1-methylxanthine (IBMX) to the bath, or ionophoretic injections of guanosine-3':5'-cyclic monophosphoric acid (cGMP) lead to depolarization of the rod membrane and an increase in the maximum peak amplitude of the receptor potential. Lowering the Ca2+ concentration or adding IBMX to the bath shifted the curve of response amplitude vs. long intensity of stimulus and sigma (intensity at half saturation) towards dimmer intensities. The ionophoresis of cGMP did not shift the position of the curve along the log stimulus intensity axis. Changing the external concentration of Ca or IBMX changes the form of the response amplitude vs. log intensity curve. This is most obvious at dim intensities. The amplitude of receptor potentials elicited by dim light was decreased by lowering Ca but increased by IBMX. The kinetics of receptor potentials were affected differently by solutions with a low Ca2+ concentration and those containing IBMX. The recovery phase of the receptor potential was slightly accelerated in the low Ca solution, whereas it was greatly slowed in the IBMX-containing solution. The ionophoretic injection of cGMP also slowed the recovery of the receptor potential. The data presented do not support the proposal that cGMP alone maintains membrane voltage in the dark and that the light-induced hydrolysis of cGMP results in the light-induced decrease in membrane conductance underlying the receptor potential. It is more likely that both Ca2+ and cGMP interact in the modulation of membrane voltage, perhaps as interrelated messengers.

1-Methyl-3-isobutylxanthine↗

PubMed1978

Ionic mechanism for the generation of horizontal cell potentials in isolated axolotl retina.

The ionic mechanism of horizontal cell potentials was investigated in the isolated retina of the axolotl Ambystoma mexicanum. The membrane potentials of both receptors and horizontal cells were recorded intracellularly while the ionic composition of the medium flowing over the receptor side of the retina was changed. The membrane potential of the horizontal cell is highly depender side of the retina was changed. The membrane potential of the horizontal cell is highly dependent on the extracellular concentration of sodium. When the external ion concentration of either chloride or potassium was changed independently of the other, there were shifts in the membrane potential of the horizontal cell which could not be explained by changes in the equilibrium potential of these ions. If the external concentrations of both potassium and chloride ions were varied so that the product of their external concentrations did not change, the shift in the membrane potential of the horizontal cell was in the direction predicted by the Nernst equation. The results are consistent with the suggestion that in the dark the receptors release a synaptic transmitter which increases primarily the sodium conductance of the horizontal cell postsynaptic membrane.

Ambystoma↗

PubMed1976

Horizontal cell potentials: dependence on external sodium ion concentration.

The membrane potential of the horizontal cell of the axolotl is highly dependent on the extracellular concentration of sodium. Experimental results reported here are consistent with the suggestion that in the dark the receptors release a synaptic transmitter which increases primarily the sodium conductance of the postsynaptic membrane. Externally applied aspartate or glutamate depolarizes the horizontal cell membrane and eliminates the light response of the horizontal cell. However, it appears to increase the conductances of the postsynaptic membrane to several ions rather than just to sodium ions.

Ambystoma↗