MaxiK channel partners: physiological impact

The basic functional unit of the large-conductance, voltage- and Ca2+-activated K+ (MaxiK, BK, BKCa) channel is a tetramer of the pore-forming alpha-subunit (MaxiK alpha) encoded by a single gene, Slo, holding multiple alternative exons. Depending on the tissue, MaxiK alpha can associate with modulatory beta-subunits (beta 1-beta 4) increasing its functional diversity. As MaxiK senses and regulates membrane voltage and intracellular Ca2+, it links cell excitability with cell signalling and metabolism. Thus, MaxiK is a key regulator of vital body functions, like blood flow, uresis, immunity and neurotransmission. Epilepsy with paroxysmal dyskinesia syndrome has been recognized as a MaxiK alpha-related disorder caused by a gain-of-function C-terminus mutation. This channel region is also emerging as a key recognition module containing sequences for MaxiK alpha interaction with its surrounding signalling partners, and its targeting to cell-specific microdomains. The growing list of interacting proteins highlights the possibility that associations with the C-terminus of MaxiK alpha are dynamic and depending on each cellular environment. We speculate that the molecular multiplicity of the C-terminus (and intracellular loops) dictated by alternative exons may modulate or create additional interacting sites in a tissue-specific manner. A challenge is the dissection of MaxiK macromolecular signalling complexes in different tissues and their temporal association/dissociation according to the stimulus.