Anion channels from rat brain synaptosomal membranes incorporated into planar bilayers

Synaptic membranes from rat brain were incorporated into planar lipid bilayers, and the characteristics of two types of anion-selective channels (type I and type II) were investigated. In asymmetric BaCl2 buffers (cis, 100 mM/trans, 25 mM), single channel conductances at -40 mV were 70 pS (type I) and 120 pS (type II). Permeability ratios (PNa:PBa:PCl) calculated from the Goldman-Hodgkin-Katz current equation for type I and type II channels were 0.23:0.04:1 and 0.05:0.03:1, respectively. Both channels exhibited characteristic voltage-dependent bursting activities. Open probability for type I channels had a maximum of approximately 0.7 at about 0 mV and decreased to zero at greater transmembrane potentials of either polarity. Type II channels were relatively voltage independent at negative voltages and were inactivated at highly positive voltages. Type I channels showed spontaneous irreversible inactivation often preceded by sudden transition to subconducting states. DIDS blocked type I channels only from the cis side, while it blocked type II channels from either side.