How many types of large conductance Ca⁺²-activated potassium channels exist in brain mitochondrial inner membrane: evidence for a new mitochondrial large conductance Ca²⁺-activated potassium channel in brain mitochondria.

Recently, we have reported electropharmacological properties of a charybdotoxin (ChTx)- and ATP-insensitive-iberiotoxin (IbTx)-sensitive large conductance Ca⁺²-activated potassium (BKCa) channel in almost purified brain mitochondrial inner membrane vesicles. In this work, we report the single-channel characterization of a new BK channel from rat brain mitochondrial inner membrane (mitochondrial large conductance Ca²⁺-activated potassium channel, mitoBKCa channel) incorporated into a planar lipid bilayer. The channel conductance was 565 pS in 200 mM KCl cis/50 mM KCl trans. The channel open probability appeared voltage-independent at -40 to +40 mV. Adding 10 mM 4-aminopyridine (4-AP) at positive and negative potentials and 2.5 mM ATP at positive voltages inhibited the channel activities. Notably, addition of 70 μM glibenclamide to the cis side had no effect on the channel behavior. Hence, it can be concluded that there are, at least, two different types of mitoBKCa channels in brain mitochondrial membrane, and the IbTx-, ChTx-, and ATP-sensitive mitoBKCa channels may be activated during the decline of cell metabolism.