Abstract
Purpose::
Potassium inward rectifying (Kir) channels play a major role in K+ regulation in the retina. These channels are responsible for the movement of K+ that generates proximal retinal ERG potentials, such as the scotopic threshold response (STR), and possibly the photopic negative response (PhNR). The Royal College of Surgeons (RCS) rat model of retinal degeneration, with a tyrosine kinase mutation, has an exaggerated electronegative STR and PhNR. We selectively suppressed Kir4.1 and Kir2.1 channel function to test their role in generating these potentials.
Methods::
We used an amphipathic protein carrier ("Chariot") to deliver Kir4.1 and Kir2.1 antibodies to intracellular epitopes in vivo. Dark and light adapted ERG’s were recorded at the cornea two hours after intravitreal injection of the antibody:Chariot complex, and eyes were then enucleated, fixed in 4% paraformaldehyde, embedded in OCT and cryosectioned for immunohistochemistry.
Results::
Intravitreal delivery of Kir4.1 antibodies reduced the STR and PhNR by about a third. Delivery of Kir2.1 antibodies produced a substantial amplitude reduction of the electronegative ERG potentials, equivalent to up to 2 log unit stimulus intensity. The Kir4.1 antibody co-localized with glial fibrillary acidic protein (GFAP) and with glutathione synthetase (GS) primarily on the Muller cells endfeet. Kir2.1 antibody labeled synaptic terminal-like formations in the inner plexiform layer that co-localized in part with protein kinase C alpha which labels depolarizing bipolar cells. This in vivo immunolabeling coincided with results of conventional in vitro immunolabeling.
Conclusions::
The results implicate Kir4.1 and Kir2.1 channels as participating in generating the electronegative STR and PhNR potentials. This provides the first in vivo evidence that Kir2.1 channels participate in regulating extracellular retinal K+ concentration, probably by K+ uptake into bipolar cells, and that Kir2.1 channels are involved in generating ERG potentials in the proximal retina.
Keywords: ion channels • electroretinography: non-clinical • retina: proximal (bipolar, amacrine, and ganglion cells)