Cloning and functional characterization of novel large conductance calcium-activated potassium channel β subunits, hKCNMB3 and hKCNMB4

We present the cloning and characterization of two novel calcium- activated potassium channel β subunits, hKCNMB3 and hKCNMB4, that are enriched in the testis and brain, respectively. We compare and contrast the steady state and kinetic properties of these β subunits with the previously cloned mouse β1 (mKCNMB1) and the human β2 subunit (hKCNMB2). Once inactivation is removed, we find that hKCNMB2 has properties similar to mKCNMB1, hKCNMB2 slows Hslo1 channel gating and shifts the current-voltage relationship to more negative potentials, hKCNMB3 and hKCNMB4 have distinct effects on slo currents not observed with mKCNMB1 and hKCNMB2. Although we found that hKCNMB3 does interact with Hslo channels, its effects on Hslo1 channel properties were slight, increasing Hslo1 activation rates. In contrast, hKCNMB4 slows Hslo1 gating kinetics, and modulates the apparent calcium sensitivity of Hslo1. We found that the different effects of the β subunits on some Hslo1 channel properties are calcium-dependent, mKCNMB1 and hKCNMB2 slow activation at 1 μM but not at 10 μM free calcium concentrations. hKCNMB4 decreases Hslo1 channel openings at low calcium concentrations but increases channel openings at high calcium concentrations. These results suggest that β subunits in diverse tissue types fine-tune slo channel properties to the needs of a particular cell.