Key result
Chimeric exchange of beta1 and beta2 subunits in BK channels demonstrated that the intracellular NH3 and COOH termini are crucial for defining subunit behavior and reducing voltage dependence.
The intracellular domains (NH3 and COOH termini) of beta1 subunits are crucial for reducing the voltage dependence of BK channels.
Identifies beta1 termini as BK voltage-dependence determinants in animals; leaves open therapeutic translation to human cardiovascular disease.
High conductance, calcium- and voltage-activated potassium (BK, MaxiK) channels are widely expressed in mammals. In some tissues, the biophysical properties of BK channels are highly affected by coexpression of regulatory (beta) subunits. The most remarkable effects of beta1 and beta2 subunits are an increase of the calcium sensitivity and the slow down of channel kinetics. However, the detailed characteristics of channels formed by alpha and beta1 or beta2 are dissimilar, the most remarkable difference being a reduction of the voltage sensitivity in the presence of beta1 but not beta2. Here we reveal the molecular regions in these beta subunits that determine their differential functional coupling with the pore-forming alpha-subunit. We made chimeric constructs between beta1 and beta2 subunits, and BK channels formed by alpha and chimeric beta subunits were expressed in Xenopus laevis oocytes. The electrophysiological characteristics of the resulting channels were determined using the patch clamp technique. Chimeric exchange of the different regions of the beta1 and beta2 subunits demonstrates that the NH3 and COOH termini are the most relevant regions in defining the behavior of either subunit. This strongly suggests that the intracellular domains are crucial for the fine tuning of the effects of these beta subunits. Moreover, the intracellular domains of beta1 are responsible for the reduction of the BK channel voltage dependence. This agrees with previous studies that suggested the intracellular regions of the alpha-subunit to be the target of the modulation by the beta1-subunit.
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Orio et al. (2006) studied this question. Chimeric constructs between beta1 and beta2 subunits was evaluated on Electrophysiological characteristics of BK channels. Chimeric exchange of beta1 and beta2 subunits in BK channels demonstrated that the intracellular NH3 and COOH termini are crucial for defining subunit behavior and reducing voltage dependence.
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