Gap junctional coupling between progenitor cells of regenerating retina in the 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 the early regeneration stage comprised one to two layers of cells with mitotic activity, progenitor cells. These cells were initially voltage-clamped at a holding potential of -80 mV, near their resting potentials, and stepped to either hyperpolarizing or depolarizing test potentials under suppression of voltage-gated membrane currents. About half the cells showed passively flowing currents that reversed polarity around their resting potentials. The currents often exhibited a voltage- and time-dependent decline. As the difference between the test potential and resting potential increased, the time until the current decreased to the steady-state level became shorter and the amount of steady-state current decreased. Thus, the overall current profile was almost symmetrical about the current at the resting potential. Input resistance estimated from the initial peak of the currents was significantly smaller than that expected in isolated progenitor cells. In a high-K(+) solution, which decreased the resting potential to around 0 mV, the symmetrical current profile was also obtained, but only when the membrane potential was held at 0 mV before the voltage steps. These observations suggest that the current was driven and modulated by the junctional potential difference between the clamping cell and its neighbors. In addition, we examined effects of uncoupling agents on the currents. A gap junction channel blocker, halothane, suppressed the currents almost completely, indicating that the currents are predominantly gap junctional currents. Furthermore, injection of biocytin into the current-recorded cells revealed tracer coupling. These results demonstrate that progenitor cells of regenerating retina couple with each other via gap junctions, and suggest the presence of their cytoplasmic communication during early retinal regeneration.