title: K+ Channel density increases selectively in the endfoot of retinal glial cells during development of Rana catesbiana.
abstract: The radial glial cells that span the retina, described by Müller in 1851, have a remarkable distribution of ion channels in adult amphibia that mediate extracellular K+ spatial buffering. 94% of the total membrane conductance of these cells resides in inward rectifier K+ channels in the endfoot processes apposed to the vitreous humour. We now report that this regional specialization is found in Müller cells isolated from adult (>120 day old) bullfrogs but to a far less extent in those from 10-20 day old tadpoles (stages 34-36). Using the cell attached configuration of the patch-clamp technique, we found, in agreement with previous studies in salamanders, that the endfoot of adult cells had 19.2+/-2.4 (mean +/- S.E., n = 81) channels/patch, whereas the soma had 1.81+/-0.28 (n = 21) channels/patch. In the tadpole, the respective values were 4.29+/-0.26 (n = 79) for the endfoot and 2.26+/-0.24 (n = 27) for the soma. The slope conductance of the inward rectifier K+ channel in 115 mM K+, 19.2+/-0.25 pS (n = 205), channel kinetics and the resting membrane potential (-69+/-2.7 mV, n = 224) were similar at both the endfoot and soma of both adults and embryos. We conclude that during development, the K+ conductance of the Müller cell endfoot, but not of the soma, increases due to a selective clustering of inwardly rectifying K+ channels in that specific region of the cell membrane. The properties of the channels change little during the transformation from tadpole to adult bullfrog.
authors.affiliation: Physiology Department and Center for Molecular and Behavioral Neuroscience, Universidad Central del Caribe, Bayamón, Puerto Rico.
authors.forename: L
authors.initials: L
authors.lastname: Rojas
authors.forename: R K
authors.initials: RK
authors.lastname: Orkand
mesh_terms: D000818:Animals; D066298:In Vitro Techniques; D007700:Kinetics; D007814:Larva / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D009431:Neural Conduction / Q000502:physiology; D009457:Neuroglia / Q000378:metabolism* / Q000648:ultrastructure; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism*; D011892:Rana catesbeiana; D012160:Retina / Q000166:cytology* / Q000254:growth & development / Q000378:metabolism*
chemical_list: D015221:Potassium Channels