Electrical coupling between glial cells in the rat retina

The strength of electrical coupling between retinal glial cells was quantif ied with simultaneous whole-cell current-clamp recordings from astrocyte-as trocyte, astrocyte-Muller cell, and Muller cell-Muller cell pairs in the ac utely isolated rat retina. Experimental results were fit and space constant s determined using a resistive model of the glial cell network that assumed a homogeneous two-dimensional glial syncytium. The effective space constan t (the distance from the point of stimulation to where the voltage falls to 1/e) equaled 12.9, 6.2, and 3.7 mum, respectively for astrocyte-astrocyte, astrocyte-Muller cell, and Muller cell-Muller cell coupling. The addition of 1 mM Ba2+ had little effect on network space constants, while 0.5 mM oct anol shortened the space constants to 4.7, 4.4, and 2.6 mum for the three t ypes of coupling. For a given distance separating cell pairs, the strength of coupling showed considerable variability. This variability in coupling s trength was reproduced accurately by a second resistive model of the glial cell network (incorporating discrete astrocytes spaced at varying distances from each other), demonstrating that the variability was an intrinsic prop erty of the glial cell network. Coupling between glial cells in the retina may permit the intercellular spread of ions and small molecules, including messengers mediating Ca2+ wave propagation, but it is too weak to carry sig nificant K+ spatial buffer currents. GLIA 35:1-13, 2001. (C) 2001 Wiley-Lis s, Inc.