Calcium-Activated Potassium Conductances in Retinal Ganglion Cells of the Ferret

Abstract

Patch-clamp recordings were made from isolated and intact retinal ganglion cells (RGCs) of the ferret to examine the calcium-activated potassium channels expressed by these neurons and to determine their functional role in the generation of spikes and spiking patterns. Single-channel recordings from isolated neurons revealed the presence of two calcium-sensitive potassium channels that had conductances of 118 and 22 pS. The properties of these two channels were shown to be similar to those ascribed to the large-conductance calcium-activated potassium channel (BKCa) and small-conductance calcium-activated potassium channel (SKCa) channels in other neurons. Whole cell recordings from isolated RGCs showed that apamin and charybdotoxin (CTX), specific blockers of the SKCa and BKCa channels, respectively, resulted in a shortening of the time to threshold and a reduction in the hyperpolarization after the spike. Addition of these blockers also resulted in a significant increase in spike frequency over a wide range of maintained depolarizations. Similar effects of apamin and CTX were observed during current-clamp recordings from intact alpha and beta ganglion cells, morphologically identified after Lucifer yellow filling. About 20% of these neurons did not exhibit a sensitivity to either blocker, suggesting the presence of functionally distinct subgroups of alpha and beta RGCs on the basis of their intrinsic membrane properties. The expression of these calcium-activated potassium channels in the majority of alpha and beta cells provides a means by which the activity of these output neurons could be modulated by retinal neurochemicals.

Intrinsic physiological properties of rat retinal ganglion cells with a comparative analysis

“…The differences we observed in frequency adaptation among different RGC types may be due to the differential expression of calcium-activated K ϩ (K Ca ) channels. These channels are well known to play a role in frequency adaptation and have been shown previously to be present in mammalian RGCs (Lipton and Tauck 1987;Wang et al 1998;Weick and Demb 2011). The high FA index exhibited by A2/alpha cells may bias the temporal properties of their well-known "transient" light responses to standing contrast (Cleland et al 1973).…”

Different Mechanisms Generate Maintained Activity in ON and OFF Retinal Ganglion Cells

“…RGCs have been reported to have differences in firing properties (transient or sustained) (Tabata and Kano, 2002) and in expression of a number of voltage-gated currents (Lipton and Tauck, 1987;Karschin and Lipton, 1989;Kaneda and Kaneko, 1991;Skaliora et al, 1993Skaliora et al, , 1995Guenther et al, 1994Guenther et al, , 1999Tabata and Ishida, 1996;Wang et al, 1997Wang et al, , 1998. These studies were done on dissociated cells, however, in which it was not possible to distinguish ON from OFF cell types.…”

Regional Differences in Distribution and Functional Expression of Small-Conductance Ca2+-Activated K+Channels in Rat Brain

“…cAMP analogues [in M: 100 cAMP or 100 8 chlorophenylthio (CPT)-cAMP] in the intracellular medium in the recording pipette (Madison and Nicoll, 1986). The SK channels are known to be predominately resistant to these drug concentrations (Ishii et al, 1997;Wang et al, 1998;Hu et al, 2001), but evidence for a small cAMP-induced increase of I aAHP has been reported (Stocker and Pedarzani, 2000). The blockade of non-SK K ϩ channels also served to increase the cell input resistance, thereby facilitating the activation of voltage-gated Ca 2ϩ channels and, hence, Ca 2ϩ influx and SK channel activation and improving the space clamp of the cell.…”