Physiological features of the S- and M-cone photoreceptors of wild-type mice from single-cell recordings

Sergei S. Nikonov, Roman Kholodenko, Janis Lem, Edward N Pugh Jr

Research output: Contribution to journalArticle

182 Citations (Scopus)

Abstract

Cone cells constitute only 3% of the photoreceptors of the wild-type (WT) mouse. While mouse rods have been thoroughly investigated with suction pipette recordings of their outer segment membrane currents, to date no recordings from WT cones have been published, likely because of the rarity of cones and the fragility of their outer segments. Recently, we characterized the photoreceptors of Nrl-/- mice, using suction pipette recordings from their "inner segments" (perinuclear region), and found them to be cones. Here we report the use of this same method to record for the first time the responses of single cones of WT mice, and of mice lacking the α-subunit of the G-protein transducin (Gtα-/-), a loss that renders them functionally rodless. Most cones were found to functionally co-express both S- (λmax = 360 nm) and M- (λ max = 508 nm) cone opsins and to be maximally sensitive at 360 nm ("S-cones"); nonetheless, all cones from the dorsal retina were found to be maximally sensitive at 508 nm ("M-cones"). The dim-flash response kinetics and absolute sensitivity of S- and M-cones were very similar and not dependent on which of the coexpressed cone opsins drove transduction; the time to peak of the dim-flash response was ∼70 ms, and ∼0.2% of the circulating current was suppressed per photoisomerization. Amplification in WT cones (A ∼4 s-2) was found to be about twofold lower than in rods (A ∼8 s-2). Mouse M-cones maintained their circulating current at very nearly the dark adapted level even when >90% of their M-opsin was bleached. S-cones were less tolerant to bleached S-opsin than M-cones to bleached M-opsin, but still far more tolerant than mouse rods to bleached rhodopsin, which exhibit persistent suppression of nearly 50% of their circulating current following a 20% bleach. Thus, the three types of mouse opsin appear distinctive in the degree to which their bleached, unregenerated opsins generate "dark light."

Original languageEnglish (US)
Pages (from-to)359-374
Number of pages16
JournalJournal of General Physiology
Volume127
Issue number4
DOIs
StatePublished - Apr 2006
Externally publishedYes

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Retinal Cone Photoreceptor Cells
Opsins
Cone Opsins
Suction
Transducin
Rhodopsin
Light
Membranes

ASJC Scopus subject areas

  • Physiology

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Physiological features of the S- and M-cone photoreceptors of wild-type mice from single-cell recordings. / Nikonov, Sergei S.; Kholodenko, Roman; Lem, Janis; Pugh Jr, Edward N.

In: Journal of General Physiology, Vol. 127, No. 4, 04.2006, p. 359-374.

Research output: Contribution to journalArticle

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abstract = "Cone cells constitute only 3{\%} of the photoreceptors of the wild-type (WT) mouse. While mouse rods have been thoroughly investigated with suction pipette recordings of their outer segment membrane currents, to date no recordings from WT cones have been published, likely because of the rarity of cones and the fragility of their outer segments. Recently, we characterized the photoreceptors of Nrl-/- mice, using suction pipette recordings from their {"}inner segments{"} (perinuclear region), and found them to be cones. Here we report the use of this same method to record for the first time the responses of single cones of WT mice, and of mice lacking the α-subunit of the G-protein transducin (Gtα-/-), a loss that renders them functionally rodless. Most cones were found to functionally co-express both S- (λmax = 360 nm) and M- (λ max = 508 nm) cone opsins and to be maximally sensitive at 360 nm ({"}S-cones{"}); nonetheless, all cones from the dorsal retina were found to be maximally sensitive at 508 nm ({"}M-cones{"}). The dim-flash response kinetics and absolute sensitivity of S- and M-cones were very similar and not dependent on which of the coexpressed cone opsins drove transduction; the time to peak of the dim-flash response was ∼70 ms, and ∼0.2{\%} of the circulating current was suppressed per photoisomerization. Amplification in WT cones (A ∼4 s-2) was found to be about twofold lower than in rods (A ∼8 s-2). Mouse M-cones maintained their circulating current at very nearly the dark adapted level even when >90{\%} of their M-opsin was bleached. S-cones were less tolerant to bleached S-opsin than M-cones to bleached M-opsin, but still far more tolerant than mouse rods to bleached rhodopsin, which exhibit persistent suppression of nearly 50{\%} of their circulating current following a 20{\%} bleach. Thus, the three types of mouse opsin appear distinctive in the degree to which their bleached, unregenerated opsins generate {"}dark light.{"}",
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