Three distinct types of voltage-dependent K super(+) channels are expressed by Mueller (glial) cells of the rabbit retina

• Published in: Pflügers Archiv 1994-01, Vol.426 (1-2), p.51-60
• Main Authors: Chao, TI, Henke, A, Reichelt, W, Eberhardt, W, Reinhardt-Maelicke, S, Reichenbach, A
• Format: Article
• Language: English
• ISSN: 0031-6768

There is ample evidence that retinal radial glial (Mueller) cells play a crucial role in retinal ion homeostasis. Nevertheless, data on the particular types of ion channels mediating this function are very rare and incomplete; this holds especially for mammalian Mueller cells. Thus, the whole-cell variation of the patch-clamp technique was used to study voltage-dependent currents in Mueller cells from adult rabbit retinae. The membrane of Mueller cells was almost exclusively permeable to K super(+) ions, as no significant currents could be evoked in K super(+)-free internal and external solutions, external Ba super(2+) reversibly blocked most membrane currents, and external Cs super(+) ions (5 mM) blocked all inward currents. All cells expressed inwardly rectifying channels that showed inactivation at strong hyperpolarizing voltages, and the conductance of which varied with the square root of extracellular K super(+) concentration ([K super(+)] sub(e)). Most cells responded to depolarizing voltages with slowly activating outward currents through delayed rectifier channels. These currents were reversibly blocked by external application of 4-aminopyridine (4-AP) or tetraethylammonium (TEA). Additionally, almost all cells showed rapidly inactivating currents in response to depolarizing voltage steps. The currents were blocked by Ba super(2+), and their amplitude increased with the [K super(+)] sub(e). Obviously, these currents belonged to the A-type family of K super(+) channels. Some of the observed types of K super(+) channels may contribute to retinal K super(+) clearance but at least some of them may also be involved in regulation of proliferative activity of the cells.