Electrophysiological Properties of Rat Retinal Mu ¨ ller (Glial) Cells in Postnatally Developing and in Pathologically Altered Retinae FELIX FELMY, 1 THOMAS PANNICKE, 2 * JU ¨ RGEN A. RICHT, 3 ANDREAS REICHENBACH, 2 AND ELKE GUENTHER 1 1 Forschungsstelle fu ¨ r Experimentelle Ophthalmologie, Universita ¨ ts-Augenklinik Abt. II, Labor fu ¨ r Zellphysiologie und Molekularbiologie, Tu ¨ bingen, Germany 2 Paul-Flechsig-Institut fu ¨ r Hirnforschung, Universita ¨ t Leipzig, Leipzig, Germany 3 Institut fu ¨ r Virologie, Justus-Liebig-Universita ¨ t, Gießen, Germany KEY WORDS patch clamp; K + channels; development; RCS rat; borna disease ABSTRACT Retinal glial Mu ¨ ller cells are characterized by dominant K + conduc- tances. The cells may undergo changes of their membrane currents during ontogeny and gliosis as described in rabbit and man. Although the rat retina is often used in physio- logical experiments, the electrophysiology of rat Mu ¨ ller cells is less well studied. The aim of the present study was to characterize their membrane currents in postnatal devel- opment and in two models of retinal degeneration. Freshly isolated cells were subjected to whole-cell patch clamp recordings. During the first 4 weeks after birth of rats, their Mu ¨ ller cells displayed an increase in all membrane currents, particularly in the inward currents elicited at hyperpolarizing potentials. The decrease of the membrane resistance from more than 760 M to less than 50 M was accompanied by a shift of the zero current potential from about -20 mV to -80 mV, similar as earlier observed in devel- oping rabbit Mu ¨ ller cells. These developmental changes were found in pigmented Brown Norway rats as well as in rats with inherited retinal dystrophy (RCS rats). Moreover, an infection of Lewis rats with the Borna disease virus caused substantial neuroretinal degeneration but did not result in a strong reduction of inward currents and of the zero current potential of the Mu ¨ ller cells. Thus, rat Mu ¨ ller cells fail to change their basic membrane properties in two different models of retinal pathology. This is in contrast to human and rabbit Mu ¨ ller cells, which have been shown to undergo dramatic changes of their membrane physiology in response to retinal diseases and injuries. GLIA 34: 190 –199, 2001. © 2001 Wiley-Liss, Inc. INTRODUCTION Mu ¨ ller cells are the dominant retinal macroglia, used in many studies describing glial functions and glio- neuronal interactions (Newman and Reichenbach, 1996). Their dominant potassium permeability enables them to perform important functions in the homeo- static regulation of the neuronal environment. Mem- brane properties of Mu ¨ ller cells were electrophysiologi- cally investigated in various species, among them salamander (Newman, 1993), turtle (LeDain et al., 1994), guinea pig (Reichelt and Pannicke, 1993), rabbit (Chao et al., 1994), and man (Reichelt et al., 1997). However, data on the functional expression of ion chan- nels on rat Mu ¨ ller cells are sparse (Ishii et al., 1997), Grant sponsor: the Bundesministerium fu ¨ r Bildung, Forschung und Technolo- gie (BMBF); Grant sponsor: Interdisciplinary Center for Clinical Research at the University of Leipzig; Grant number: 01KS9504, Project C5; Grant sponsor: fortu ¨ ne-programme Tu ¨ bingen; Grant sponsor: the Deutsche Forschungsgemein- schaft; Grant number: Project PA 615/1-1. The current address of Juergen A. Richt is United States Department of Agriculture, Agricultural Research Service, National Animal Disease Center, 2300 Dayton Road, Ames, Iowa 50010 *Correspondence to: Thomas Pannicke, Paul-Flechsig-Institut fu ¨ r Hirnfors- chung, Universita ¨ t Leipzig, Jahnallee 59, D-04109 Leipzig, Germany. E-mail: pant@medizin.uni-leipzig.de Received 25 January 2001; Accepted 15 March 2001 GLIA 34:190 –199 (2001) © 2001 Wiley-Liss, Inc.