Gap junctional coupling between progenitor cells of regenerating retina inthe adult newt

Gap junctional coupling between progenitor cells of regenerating retina in the adult newt was examined by a slice-patch technique. Retinal slices at t he early regeneration stage comprised one to two layers of cells with mitot ic activity, progenitor cells. These cells mere initially voltage-clamped a t a holding potential of -80 mV, near their resting potentials, and stepped to either hyperpolarizing or depolarizing test potentials under suppressio n of voltage-gated membrane currents. About half the cells showed passively flowing currents that reversed polarity around their resting potentials. T he currents often exhibited a voltage- and time-dependent decline. As the d ifference between the test potential and resting potential increased, the t ime until the current decreased to the steady-state level became shorter an d the amount of steady-state current decreased. Thus, the overall current p rofile was almost symmetrical about the current at the resting potential. I nput resistance estimated from the initial peak of the currents was signifi cantly smaller than that expected in isolated progenitor cells. In a high-K + solution, which decreased the resting potential to around 0 mV, the symme trical current profile was also obtained, but only when the membrane potent ial was held at 0 mV before the voltage steps. These observations suggest t hat the current was driven and modulated by the junctional potential differ ence between the clamping cell and its neighbors. In addition, we examined effects of uncoupling agents on the currents. A gap Junction channel blocke r, halothane, suppressed the currents almost completely, indicating that th e currents are predominantly gap junctional currents. Furthermore, injectio n of biocytin into the current-recorded cells revealed tracer coupling. The se results demonstrate that progenitor cells of regenerating retina couple with each other via gap junctions, and suggest the presence of their cytopl asmic communication during early retinal regeneration. (C) 2000 John Wiley & Sons, Inc.