MaxiK channels are large conductance, voltage and calcium-sensitive potassium channels which are fundamental to the control of smooth muscle tone and neuronal excitability. MaxiK channels can be formed by 2 subunits: the pore-forming alpha subunit and the modulatory beta subunit. The protein encoded by this gene is an auxiliary beta subunit which may partially inactivate or slightly decrease the activation time of MaxiK alpha subunit currents. Alternative splicing results in multiple transcript variants. A related pseudogene has been identified on chromosome 22. [provided by RefSeq, Jul 2009],
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Function:
Domain:The cytoplasmic N-terminus domain of isoform 4 participates in the partial inactivation of KCNMA1, possibly by binding to a receptor site.,Domain:The extracellular domain forms gates to block ion permeation, providing a mechanism by which current can be rapidly diminished upon cellular repolarization.,Function:Regulatory subunit of the calcium activated potassium KCNMA1 (maxiK) channel. Modulates the calcium sensitivity and gating kinetics of KCNMA1, thereby contributing to KCNMA1 channel diversity. Alters the functional properties of the current expressed by the KCNMA1 channel. Isoform 2, isoform 3 and isoform 4 partially inactivate the current of KCNBMA. Isoform 4 induces a fast and incomplete inactivation of KCNMA1 channel that is detectable only at large depolarizations. In contrast, isoform 1 does not induce detectable inactivation of KCNMA1. Two or more subunits of KCNMB3 are required to block the KCNMA1 tetramer.,PTM:N-glycosylated.,PTM:The extracellular domain contains disulfide bond essential for the gating mechanism.,similarity:Belongs to the KCNMB family.,subunit:Interacts with KCNMA1 tetramer. There are probably 4 molecules of KCMNB3 per KCNMA1 tetramer.,tissue specificity:Isoform 1, isoform 3 and isoform 4 are widely expressed. Isoform 2 is expressed placenta, pancreas, kidney and heart. Isoform 1 and isoform 3 are highly expressed in pancreas and testis.,
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Cellular Localization:
Membrane; Multi-pass membrane protein.
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Tissue Expression:
Isoform 1, isoform 3 and isoform 4 are widely expressed. Isoform 2 is expressed placenta, pancreas, kidney and heart. Isoform 1 and isoform 3 are highly expressed in pancreas and testis.