EFFECT OF CUTTING THE OPTIC-NERVE ON K+ CURRENTS IN ENDFEET OF MULLERCELLS ISOLATED FROM FROG RETINA

Membrane currents were recorded from Muller cells isolated from normal retinas and from retinas whose ganglion cell axons had been cut in th e optic nerve 30-60 days previously. The surgical procedure did not bl ock the retinal blood supply and did not allow the axons to regenerate . The principal finding was that after severing the optic nerve there was less inward rectification in response to voltage commands. That is , the maintained inward current (I-K(IN)) produced in response to a hy perpolarizing voltage command decreased leading to a decrease in the r atio I-K(IN)/I-K(OUT). In 98 mM [K+](0), this ratio was 2.86 +/- 0.21 (mean +/- SE; n = 24) in controls and 1.13 +/- 0.13 (n = 21) in Muller cells from denervated retinae. Barium, a blocker of the potassium inw ard rectifier (I-KIR), eliminated this difference. Moreover, severing the optic nerve also decreased the resting potentials of Muller cells in 2.5 mM [K+](0) from -83 +/- 7 mV to -63 +/- 9 mV. The results sugge st that the voltage-dependent behavior and selectivity of K+ inward re ctifying channels (K-ir) in the endfeet depends on the integrity of th e closely apposed ganglion cells.