The single-channel behavior of the hyperpolarization-activated, ClC-2-like inwardly rectifying Cl− current (I Clh), induced by long-term dibutyryl-cyclic-AMP-treated cultured cortical rat astrocytes, was analyzed with the patch-clamp technique. In outside-out patches in symmetrical 144 mM Cl− solutions, openings of hyperpolarization-activated small-conductance Cl− channels revealed burst activity of two equidistant conductance levels of 3 and 6 pS. The unitary openings displayed slow activation kinetics. The probabilities of the closed and conducting states were consistent with a double-barrelled structure of the channel protein. These results suggest that the astrocytic ClC-2-like Cl− current I Clh is mediated by a small-conductance Cl− channel, which has the same structural motif as the Cl− channel prototype ClC-0.
