Switch of K + buffering conditions in rabbit retinal Müller glial cells during postnatal development

Abstract

Although spatial buffering of excess extracellular K + by K + channels is a main function of retinal glial (Müller) cells, there are severe limitations to long distance K +-spatial buffering that have been predicted for (immature) glial cells: (i) a lack of inwardly rectifying K + (Kir) channels [Glia 21(1997) 46]; and (ii) high internal resistance of outgrowing (cable like) processes [W. Rall, Handbook of Physiology, Section 1, vol. 1, Part 1, American Physiological Society, Bethesda, 1977, pp. 39–97]. In order to determine if changes in developing Müller cells improve or worsen their capability of carrying K + spatial buffering currents, we compared the whole-cell currents of acutely isolated Müller cells at 5, 11 and 28 postnatal days of rabbits. Both K +-spatial buffer limitations described above were found in early postnatal stage (5 days), however, the cells overcome these limitations shortly after 11 days. During the period of 11–28 days, rabbit Müller cells simultaneously increase stalk axial conductance and express Kir channels. Both processes take place during the critical stage of retinal maturation, and should dramatically improve “cable” K +-spatial buffering.