Ionic currents of cultured horizontal cells isolated from white perch retina

Abstract

Horizontal cells from the retinas of white perch were isolated and maintained in cell culture for 3 days to 3 wk. Four morphologically distinct types of horizontal cells could be identified in culture and were labeled types H1, H2, H3, and H4. Whole-cell patch-clamp techniques were used to study the ionic currents present in the four cell types. In all cells, depolarizing commands above threshold elicited a fast-inward current followed by an outward current. The fast-inward current was abolished by tetrodotoxin (TTX) or 0 Na+ Ringer's, indicating the current was carried by Na+. In H1, H2, and H3 cells, the outward current, carried by K+, consisted of two components: a transient current (IA), blockable with 4-aminopyridine (4-AP), tetraethylammonium (TEA), or intracellular cesium and a sustained current that could be blocked with TEA. The H4 cell had only the sustained current. An inward rectifying K+ current (anomalous rectifier) was observed in the four cell types. The current was sensitive to the extracellular K+ concentration. Its activation showed two components: an instantaneous component and a slower component. The slow component becomes faster with greater hyperpolarizations. The four cell types possessed a small, sustained Ca2+ current that, under normal conditions, was masked by the inward Na+ current and outward K+ currents.

A slowly inactivating potassium current truncates spike activity in ganglion cells of the tiger salamander retina

“…We found no evidence for voltage-gated currents at potentials more negative than the resting level of the cell, yet horizontal cells (Lasater, 1986) and bipolar cells (Kaneko and Tachibana, 1985) appear to have these currents. The inset in Figure 3B shows that over the voltage range from -80 to -150 mV the cell had a linear conductance of 0.9 nS, or an input resistance of 1.1 GO.…”

“…The current-voltage relation for the complete set of transient inward currents, measured at the response peak, is shown in Figure 4B. The current began to activate at potentials more positive than -40 mV and reached a maximum of 739 pA near -15 mV, similar to that of other membranes (Cole and Moore, 1960;Lasater, 1986;Lipton and Tauck, 1987). The reversal potential for this current was near +45 mV.…”

“…Of the 24 cells studied, activation began between -45 and -30 mV. Selected currents The current-voltage relationship, measured at the peak reother retinal cells (Kaneko and Tachibana, 1985;Lasater, 1986; sponse, for the complete set of voltage steps is shown in Figure Lipton and Tauck, 1987). For potentials more positive than -5 6B.…”

Proton-Mediated Feedback Inhibition of Presynaptic Calcium Channels at the Cone Photoreceptor Synapse

“…At the holding potential of Ϫ60 mV, the reduction in current from 94 to 60 pA was significant. Glutamate has complex effects on HCs, modulating inward rectification (Kaneko and Tachibana, 1985), increasing AMPA and kainate receptor activity (Lasater, 1986;Shingai and Christensen, 1986), suppressing Ca channel activity via intracellular acidification (Dixon et al, 1993), and enhancing outward rectification (Tachibana, 1983). We are not yet certain of the identity of the amiloride-sensitive conductance, and it will require investigation beyond the scope of this present work to be determined.…”

Neuromodulation of ligand- and voltage-gated channels in the amphibian retina

“…For example, in response to a bright light flash of appropriate wavelength, the horizontal cell membrane is driven beyond Ϫ70 mV, a voltage sufficient to activate a transient potassium channel (Lasater, 1986;Malchow and Ripps, 1990;Tachibana, 1983). At light offset, moreover, horizontal cells often respond with a spike-like depolarization whose kinetics are influenced by the parameters of the light stimulus, and by the activity of voltage-dependent calcium channels in the horizontal cell membrane (Akopian et al, 1997;Normann and Perlman, 1979;Stone and Witkovsky, 1987).…”