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J. Xu, M.M. Slaughter; Light-evoked Gap-junction Current between Rods in Salamander Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4156.
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Purpose: In tiger salamander retina, rods are well coupled by gap-junctions. The coupling is proposed to increase light response amplitude of single rods and decrease noise. We measured the current going through gap-junctions between rods, especially in response to light. Methods: We combined voltage-clamp methods and gap-junction blockers to record the gap-junction current from rods in dark-adapted salamander retinal slices. The rationale is that voltage-clamp of rod somas isolates rod terminals from the photocurrent from the outer segment, and thus any voltage dependent current is from other photoreceptors through gap junctions near the synaptic terminal. Results: We found the rod light response had a spike like overshoot at light offset when 40 mM TEA was used to block potassium channels. This spike was blocked by a gap-junction blocker, carbenoxolone, and was dependent on calcium and calcium activated chloride currents. In normal Ringer, the spike was rare. Instead a slower and smaller overshoot occurred, which was blocked by niflumic acid, a calcium-activated chloride channel blocker, and reduced by carbenoxolone. We also noted that some rods had a small transient outward current at light onset. Carbenoxolone suppressed this transient current, slowing the light response. In rods without outer segments there was still a light response. The response was smaller and with a more rapid decay, but with the same polarity as the normal light response. This fast, transient light response was blocked by carbenoxolone. Conclusion: We found that gap junctions between rods affect rod membrane potential and shape the light response. A fast transient component of the light response is carried through gap junction channels. This current is probably dependent on calcium-activated chloride current.
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