Contribution of pannexin channels to afterimage signals in the amphibian retina.

Pannexin 1 (Panx1) forms large-pore, single-membrane channels that connect the intracellular and extracellular environments, permitting the passage of ions and small molecules, such as ATP. Panx1 channels are involved in diverse signaling pathways that contribute to various physiological processes, including sensory processing, although their precise mechanisms of action remain incompletely understood. This study reveals a Panx1-mediated mechanism regulating visual signal processing in the amphibian retina. Using immunolabeling and confocal imaging, we localized Panx1 channels in the cone-dominated On-bipolar cells, specifically at both somas and axon terminals. Whole cell patch-clamp recordings showed that these channels have high permeability to Cl ions, which can be blocked by Panx1 peptide, carbenoxolone, and mefloquine, all recognized as Panx1 inhibitors. Blocking Panx1 channels or reducing external Cl concentrations significantly increased bright light-induced delayed spontaneous excitatory responses in ganglion cells, indicating an inhibitory role of Panx1 channels at the bipolar cell synaptic release. These delayed spontaneous responses in ganglion cells, known as rebound currents, are associated with afterimage signals in the retina. Our findings suggest that Panx1 channels help prevent overexcitation associated with bright light-induced afterimage phenomena. Cl permeable Panx1 channels in the On-bipolar cells serve as a novel mechanism for the negative control of overexcitation in afterimage signal processing in the retina.