EVIDENCE FOR HEMI-GAP JUNCTIONAL CHANNELS IN ISOLATED HORIZONTAL CELLS OF THE SKATE RETINA

Prolonged depolarization of isolated, voltage-clamped skate retinal ho rizontal cells produces an outward current that exhibits a late onset and develops slowly with time. This current, which we refer to as the Q-current, is associated with an increase in membrane conductance, and is present when other voltage-gated conductances have been pharmacolo gically blocked. The reversal potential for the Q-current, obtained us ing tail current analysis, was close to 0 mV. The magnitude of the cur rent was greatly reduced by superfusion with 25 mM acetate, and by 4 m M cobalt chloride, 2 mM 1-octanol, and a saturated solution of the gen eral anesthetic halothane. In addition, the low-molecular weight fluor escent dye Lucifer yellow, applied extracellularly, entered the cells during activation of the Q-current, whereas a 3 kD dextran-fluorescein complex did not cross the cell membrane. The effects of divalent cati ons, the non-specific nature of the ionic current suggested by its rev ersal potential, the entry of Lucifer yellow, and the ability of aceta te, halothane, cobalt, and octanol to block the current lead us to hyp othesize that the Q-current results from the opening of hemi-gap junct ional channels that mediate electrical coupling between skate horizont al cells.