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Characterization of BK channel splice variants using membrane potential dyes
Author(s) -
Saleem F,
Rowe ICM,
Shipston MJ
Publication year - 2009
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.2008.00011.x
Subject(s) - bk channel , ionomycin , splice , hyperpolarization (physics) , membrane potential , chemistry , patch clamp , voltage dependent calcium channel , biology , calcium , microbiology and biotechnology , biophysics , biochemistry , intracellular , gene , receptor , nuclear magnetic resonance spectroscopy , organic chemistry
Background and purpose: Large conductance calcium‐ and voltage‐activated potassium (BK) channels are encoded by a single gene that displays extensive pre‐mRNA splicing. Here we exploited a membrane potential assay to investigate the sensitivity of different BK splice variants to elevations in intracellular free calcium and their inhibition by the BK channel blocker paxilline. Experimental approach: Murine BK channel splice variants were expressed in human embryonic kidney 293 cells and their properties analysed in response to ionomycin‐induced calcium influx in both fluorescent membrane potential (fluorescent‐imaging plate reader) and patch clamp electrophysiological assays. The dose‐dependent inhibition of distinct splice variants by the BK channel‐specific blocker paxilline was also investigated. Key results: Ionomycin‐induced calcium influx induced a robust hyperpolarization of human embryonic kidney 293 cells expressing distinct BK channel splice variants: stress regulated exon (STREX), e22 and ZERO. Splice variant expression resulted in membrane hyperpolarization that displayed a rank order of potency in response to calcium influx of STREX > e22 > ZERO. The BK channel inhibitor paxilline exhibited very similar potency on all three splice variants with IC 50 s in membrane potential assays of 0.35 ± 0.04, 0.37 ± 0.03 and 0.70 ± 0.02 µmol·L −1 for STREX, ZERO and e22 respectively. Conclusions and implications: BK channel splice variants can be rapidly discriminated using membrane potential based assays, based on their sensitivity to calcium. BK channel splice variants are inhibited by the specific blocker paxilline with similar IC 50 s. Thus, paxilline may be used in functional assays to inhibit BK channel function, irrespective of the variant expressed.