sloβ2 is a member the regulatory β subunit family that controls the activity of the large conductance Ca2+-activated K+ channel KCa1.1. This family includes four members with a shared topology: two trans-membrane domains, short intracellular N- and C-termini and a large extracellular region and a distinct tissue distribution. sloβ2 expression is relatively broad and includes expression in brain, heart, kidney adrenal chromaffin cells and ovary.
The KCa1.1 K+ channel can be activated by either an increase in intracellular Ca2+ concentration or by membrane depolarization. The regulatory β subunits increase the sensitivity of the pore-forming KCa1.1 subunit to Ca2+ and membrane voltage and they may also change the channel pharmacology.
The sloβ2 subunit is unique in that it is able to induce a rapid and complete inactivation of the KCa1.1 channel in a manner that closely resembles the ball-and-chain inactivation of the voltage-dependent K+ (Kv) channels. In other words, the inactivation is dependent on a sequence in the N-terminal part of the sloβ2 subunit that appears to block the mouth of the ion permeation pathway.
The physiological significance of the sloβ2 subunit is not clear, but it appears to participate in the inactivation of the KCa1.1 channel in hippocampal CA1 neurons and adrenal chromaffin cells.
