Potassium Spatial Buffering - Potassium Siphoning

Potassium Siphoning

Potassium spatial buffering that occurs in the retina is called potassium siphoning, where the Muller cell is the principal glial cell type. Muller cells have important role in retinal physiology. It maintains retinal cell metabolism and are critical in maintaining potassium homeostasis in extracellular space during neuronal activity. Like cells responsible for spatial buffering, Muller cells are distinctively permeable to potassium ions through Kir channels. Like other glial cells, the high selectivity of Muller cell membranes to potassium ions is due to the high density of Kir channels. Potassium conductance is unevenly distributed in Muller cells. By focally increasing potassium ions along amphibian Muller cells and recording the resulting depolarization, the observed potassium conductance was concentrated in the endfoot process of 94% of the total potassium conductance localized to the small subcellular domain. The observation lead to hypothesis that excess potassium in extracellular space is “siphoned” by the Muller cells to the vitreous humor. Potassium siphoning is a specialized form of spatial buffering mechanisms where large reservoir of potassium ions is emptied into vitreous humor. Similar distribution patter of Kir channels could be found in amphibians.