Purchase this article with an account.
Wen Shen, Lauren A. Purpura, Changlong Nan, Irene Chang, Harris Ripps; Regulation of Synaptic Transmission at the Photoreceptor Terminal: A Novel Role for the Cation-Chloride Cotransporter NKCC1. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5267.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Previously, we demonstrated that NKCC1 is expressed predominantly in the photoreceptor terminals and horizontal cells of the distal retina. Since NKCC1 serves to uptake Cl- and thereby increase the ECl in neurons, we studied how these properties affected synaptic transmission between photoreceptors and second-order neurons. In addition, we explored the factors that change the levels of NKCC1 expression in retina.
Whole cell patch clamp recordings were obtained from photoreceptors and horizontal cells in tiger salamander retinal slices. Voltage- and light-evoked current responses were recorded from those neurons before and after applying bumetanide to block endogenous NKCC1 activity in the distal retina. Standard q-PCR and Western blot assays were performed to determine NKCC1 mRNA and protein levels in dark- and light-adapted retinas, as well as in retinas treated with dopamine and its agonist and antagonist.
Recordings from postsynaptic horizontal cells revealed that inhibiting NKCC1 with bumetanide greatly increased glutamate release from both rod and cone terminals. Ca2+ channel current recordings and capacitance measurements showed that NKCC1 directly regulates Ca2+ -dependent exocytosis at the photoreceptor synapse, and raises the possibility that NKCC1 serves to suppress the vesicular release of glutamate from photoreceptor terminals in dark and at light offset. Interestingly, NKCC1 gene and protein expression were up-regulated by light, which we attribute to the light-induced release of dopamine acting on D1 receptors.
Our study reveals a new role for NKCC1 in the regulation of synaptic transmission at photoreceptor terminals. NKCC1 appears to protect the retina from glutamate toxicity due to excessive vesicle release, and serves also to optimize synaptic gain in the distal retina. Light adaptation, acting through a dopaminergic pathway, increases NKCC1 expression levels, which probably results in increased NKCC1 activity in photoreceptor terminals and horizontal cells.
This PDF is available to Subscribers Only