Both transmembrane domains of BK β1 subunits are essential to confer the normal phenotype of β1-containing BK channels

Guruprasad Kuntamallappanavar, Ligia Toro, Alejandro Dopico

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

Voltage/Ca2+ i-gated, large conductance K+ (BK) channels result from tetrameric association of a (slo1) subunits. In most tissues, BK protein complexes include regulatory β subunits that contain two transmembrane domains (TM1, TM2), an extracellular loop, and two short intracellular termini. Four BK β types have been identified, each presenting a rather selective tissue-specific expression profile. Thus, BK β modifies current phenotype to suit physiology in a tissue-specific manner. The smooth muscle-abundant BK β1 drastically increases the channel's apparent Ca2+ i sensitivity. The resulting phenotype is critical for BK channel activity to increase in response to Ca2+ levels reached near the channel during depolarization-induced Ca2+ influx and myocyte contraction. The eventual BK channel activation generates outward K+ currents that drive the membrane potential in the negative direction and eventually counteract depolarization-induced Ca2+ influx. The BK β1 regions responsible for the characteristic phenotype of β1-containing BK channels remain to be identified. We used patch-clamp electrophysiology on channels resulting from the combination of smooth muscle slo1 (cbv1) subunits with smooth muscle-abundant β1, neuron-abundant β4, or chimeras constructed by swapping β1 andβ4 regions, and determined the contribution of specific β1 regions to the BK phenotype. At Ca2+ levels found near the channel during myocyte contraction (10 mM), channel complexes that included chimeras having both TMs from β1 and the remaining regions ("background") from β4 showed a phenotype (Vhalf, τact, τdeact) identical to that of complexes containing wtβ1. This phenotype could not be evoked by complexes that included chimeras combining either β1 TM1 or β1 TM2 with a β4 background. Likewise, β "halves" (each including β1 TM1 or β1 TM2) resulting from interrupting the continuity of the EC loop failed to render the normal phenotype, indicating that physical connection between β1 TMs via the EC loop is also necessary for proper channel function.

Original languageEnglish (US)
Article number109306
JournalPloS one
Volume9
Issue number10
DOIs
StatePublished - Oct 2 2014

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Large-Conductance Calcium-Activated Potassium Channels
Phenotype
Muscle
phenotype
calcium
Depolarization
Tissue
chimerism
smooth muscle
Smooth Muscle
Electrophysiology
Physiology
Clamping devices
myocytes
Muscle Cells
Neurons
Chemical activation
Association reactions
electrophysiology
Membranes

All Science Journal Classification (ASJC) codes

  • Biochemistry, Genetics and Molecular Biology(all)
  • Agricultural and Biological Sciences(all)

Cite this

Both transmembrane domains of BK β1 subunits are essential to confer the normal phenotype of β1-containing BK channels. / Kuntamallappanavar, Guruprasad; Toro, Ligia; Dopico, Alejandro.

In: PloS one, Vol. 9, No. 10, 109306, 02.10.2014.

Research output: Contribution to journalArticle

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