Voltage-clamp recordings of light responses from wild-type and mutant mouse cone photoreceptors

作者：Norianne T. Ingram, Alapakkam P. Sampath, Gordon Fain · 发表于：The Journal of General Physiology · 年份：2019 · DOI：10.1085/jgp.201912419 · 被引用次数：56 · 研究领域：Retinal Development and Disorders、Photoreceptor and optogenetics research、Neuroscience and Neuropharmacology Research

We describe the first extensive study of voltage-clamp current responses of cone photoreceptors in unlabeled, dark-adapted mouse retina using only the position and appearance of cone somata as a guide. Identification was confirmed from morphology after dye filling. Photocurrents recorded from wild-type mouse cones were biphasic with a fast cone component and a slower rod component. The rod component could be eliminated with dim background light and was not present in mouse lines lacking the rod transducin-α subunit (Gnat1−/−) or connexin 36 (Cx36−/−). Cones from Gnat1−/− or Cx36−/− mice had resting membrane potentials between −45 and −55 mV, peak photocurrents of 20–25 picoamps (pA) at a membrane potential Vm = −50 mV, sensitivities 60–70 times smaller than rods, and a total membrane capacitance two to four times greater than rods. The rate of activation (amplification constant) was largely independent of the brightness of the flash and was 1–2 s−2, less than half that of rods. The role of Ca2+-dependent transduction modulation was investigated by recording from cones in mice lacking rod transducin (Gnat1), recoverin, and/or the guanylyl-cyclase–activating proteins (GCAPs). In confirmation of previous results, responses of Gnat1−/−;Gcaps−/− cones and triple-mutant Gnat1−/−;Gcaps−/−;Rv−/− cones recovered more slowly both to light flashes and steps and were more sensitive than cones expressing the GCAPs. Cones from all four mouse lines showed significant recovery and escaped sa...