VOLTAGE-GATED CURRENTS IN RABBIT RETINAL ASTROCYTES

The voltage-gated currents of the astrocytes associated with the retinal capillaries of the rabbit retina were studied using whole-cell patch clamp recording. The resting potential of these cells was -70 +/- 4.8 mV (mean +/- SEM; n = 54), and the input resistance and cell capacitance were 558 +/- 3.6 M Omega and 19.5 +/- 1.8 pF respectively. Depolarization to potentials positive to -50 mV evoked rapidly activating inward and outward currents. The inward current was transient, eliminated by substitution of choline for Na+ in the bathing solution, and reduced by 50% in the presence of 1 mu M tetrodotoxin. The time-to-peak of the Na+ current was more than twice that for the Na+ current found in retinal neurons. The glial Na+ current was half-inactivated at -55 mV. A transient component of the outward K+ current was blocked by external 4-aminopyridine while a more sustained component was blocked by external tetraethylammonium. At potentials between -150 and -50 mV the membrane behaved Ohmically. Voltage-gated currents in retinal astrocytes recorded in situ appear qualitatively similar to those described for some glial cells in vitro.