REGULATION OF K-STELLATE CELL (TTT( CHANNELS BY CELL CONTACT IN A CLONED FOLLICULO)GF)/

Membrane currents in a folliculo-stellate cell line (TtT/GF) were exam ined using the whole-cell clamp technique. The cultured cells were mor phologically categorized as isolated spread cells, isolated round cell s, contact spread cells, and contact round cells. A distinct outward c urrent was observed in isolated spread cells, contact round cells, and contact spread cells, whereas the outward current detected in isolate d round cells was barely perceivable. The reversal potentials of the o utward tail current obeyed the Nernst equation, indicating that the ou tward current was carried by K+ ions. The activation and deactivation processes of the K+ current could be fitted by single exponential curv es. 4-aminopyridine, tetraethylammonium, and Ba2+ inhibited the K+ cur rent. The concentrations for half-maximal inhibition of these agents t o block the K+ current were 0.2 mM, 0.8 mM, and 8 mM, respectively. Th e biophysical and pharmacological characteristics of the K+ current in TtT/GF cells were similar to those of the K+ current in glial and Sch wann cells. According to the results of the present study, it was conc luded that TtT/GF cells possessed outward K+ channels, characteristics of which were similar to those of the K+ channels in glial and Schwan n cells, and that the amplitude of the K+ current in TtT/GF cells seem ed to be regulated by the condition of the cell contact.