Measurement of potassium turnover in rod photoreceptors in toad isolated retina using ion-selective microelectrodes

Ion-selective microelectrodes (ISMs) were used to measure the turnover of intracellular K+[Formula: see text] in rods in the isolated retina of the toad, Bufo marinus. The light-evoked hyperpolarization of rods decreases their passive K+ efflux, which in combination with active K+ uptake, decreases extracellular K+ concentration, [Formula: see text]. Rb+ substitutes for K+ in these processes. The turnover of [Formula: see text] was measured as Rb+ and K+ were exchanged, using ISMs that were approximately five times more sensitive to Rb+ than to K+. When [Formula: see text]was replaced by [Formula: see text], the light-evoked decrease in K+ efflux produced only a small change in ISM voltage, ΔVISM, owing to the background of [Formula: see text]. As [Formula: see text] replaced [Formula: see text], the efflux shifted from K+ to Rb+ and ΔVISM grew in amplitude. After loading the rods with [Formula: see text], [Formula: see text] was replaced by [Formula: see text]. The light-evoked decrease in Rb+ efflux lead transiently to a large ΔVISM, since the change in [Formula: see text], was superimposed upon a background of [Formula: see text]. As [Formula: see text] replaced [Formula: see text], the amplitude of ΔVISM declined. When measured using this technique, the turnover of [Formula: see text] was 95% complete in approximately 15 min. In low Ca2+ solutions, transmembrane fluxes of K+ (Rb+) increased and turnover of [Formula: see text] occurred more rapidly. During background illumination, transmembrane fluxes of K+ (Rb+) decreased and turnover of [Formula: see text] was slowed. These experiments have provided independent corroboration of earlier observations concerning rod K+ fluxes. This ISM-based technique also may be useful in measuring K+ turnover in other cell types.

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Photoreceptor coupling in retina of the toad, Bufo marinus. I. Anatomy

Journal of Neurophysiology ◽

10.1152/jn.1979.42.1.292 ◽

1979 ◽

Vol 42 (1) ◽

pp. 292-310 ◽

Cited By ~ 41

Author(s):

G. H. Gold ◽

J. E. Dowling

Keyword(s):

Gap Junctions ◽

Freeze Fracture ◽

Bufo Marinus ◽

Physiological Data ◽

Dense Network ◽

Rod Photoreceptors ◽

Rods And Cones ◽

Toad Bufo

1. Red rod photoreceptors in the toad retina, which are known to be physiologically coupled, were examined for interreceptor contacts. 2. A dense network of large gap junctions was found between the inner segments of red rods, this being the only specialized site of contact that was observed between rods. Each red rod contacts an average of about four neighboring red rods with a junctional area of approximately 0.75 micrometer2. From freeze-fracture micrographs, the density of junctional particles was found to be 5 X 10(3)/micrometer2. 3. The large gap junctions were found only to connect red rods to each other in agreement with physiological data. Only small focal gap junctions were seen between red rods and cones and no junctions were observed between red and green rods. 4. It is concluded that these gap junctions are the site of coupling between the red rods and that the coupling is electrical.

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Decline of electrogenic Na+/K+ pump activity in rod photoreceptors during maintained illumination.

The Journal of General Physiology ◽

10.1085/jgp.87.4.633 ◽

1986 ◽

Vol 87 (4) ◽

pp. 633-647 ◽

Cited By ~ 12

Author(s):

H Shimazaki ◽

B Oakley

Keyword(s):

Membrane Resistance ◽

Membrane Voltage ◽

Continuous Illumination ◽

Subretinal Space ◽

Rod Photoreceptors ◽

Pharmacological Agents ◽

Pump Activity ◽

Isolated Retina ◽

Voltage Dependent ◽

Toad Bufo

Light-evoked changes in membrane voltage were recorded intracellularly from rod photoreceptors in the isolated retina preparation of the toad, Bufo marinus, during superfusion with a solution containing pharmacological agents that blocked voltage-dependent conductances. Under these conditions, the amplitude of the hyperpolarizing photoresponse became much greater than under control conditions. The results of several experiments support the conclusion that this increase in photoresponse amplitude was due primarily to a voltage that was produced when the electrogenic current from the rods' Na+/K+ pump flowed across an increased membrane resistance (Torre, V. 1982. Journal of Physiology. 333:315). At the onset of a period of continuous illumination, the rod membrane first hyperpolarized and then began to repolarize, and after 180 s of illumination, the membrane voltage had recovered by 60-72% of its initial hyperpolarization. There did not appear to be any significant decrease in rod membrane resistance associated with this repolarization. Both the enhanced hyperpolarization at light onset and the slow repolarization during maintained illumination were blocked by superfusion with 10.0 microM strophanthidin. These data support the hypothesis that the activity of the rods' Na+/K+ pump declines progressively during maintained illumination. It is likely that the decline in pump activity produces significant changes in [K+]o in the subretinal space during maintained illumination.

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