Molecular identification of Ca2+-activated K+ channels in parotid acinar cells.
We used molecular biological and patch-clamp techniques to identify the Ca(2+)-activated K(+) channel genes in mouse parotid acinar cells. Two types of K(+) channels were activated by intracellular Ca(2+) with single-channel conductance values of 22 and 140 pS (in 135 mM external K(+)), consistent with the intermediate and maxi-K classes of Ca(2+)-activated K(+) channels, typified by the mIK1 (Kcnn4) and mSlo (Kcnma1) genes, respectively. The presence of mIK1 mRNA was established in acinar cells by in situ hybridization. The electrophysiological and pharmacological properties of heterologously expressed mIK1 channels matched those of the native current; thus the native, smaller conductance channel is likely derived from the mIK1 gene. We found that parotid acinar cells express a single, uncommon splice variant of the mSlo gene and that heterologously expressed channels of this Slo variant had a single-channel conductance indistinguishable from that of the native, large-conductance channel. However, the sensitivity of this expressed Slo variant to the scorpion toxin iberiotoxin was considerably different from that of the native current. RT-PCR analysis revealed the presence of two mSlo beta-subunits (Kcnmb1 and Kcnmb4) in parotid tissue. Comparison of the iberiotoxin sensitivity of the native current with that of parotid mSlo expressed with each beta-subunit in isolation and measurements of the iberiotoxin sensitivity of currents in cells from beta(1) knockout mice suggest that parotid acinar cells contain approximately equal numbers of homotetrameric channel proteins from the parotid variant of the Slo gene and heteromeric proteins composed of the parotid Slo variant in combination with the beta(4)-subunit.
Nehrke
Keith
K
Center for Oral Biology, Aab Institute of Biomedical Sciences, and Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York 14642, USA.
Quinn
Claire C
CC
Begenisich
Ted
T
D017398:Alternative Splicing / Q000187:drug effects / Q000235:genetics; D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D001483:Base Sequence / Q000235:genetics; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D002478:Cells, Cultured; D006224:Cricetinae; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051038:Large-Conductance Calcium-Activated Potassium Channel beta Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D018721:Muscarinic Agonists / Q000494:pharmacology; D009154:Mutation / Q000187:drug effects / Q000235:genetics; D010306:Parotid Gland / Q000166:cytology / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D012472:Salivation / Q000187:drug effects / Q000235:genetics
D015220:Calcium Channels; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C494841:KCNMA1 protein, human; C496923:KCNN4 protein, human; C494843:Kcnmb4 protein, mouse; C496925:Kcnn4 protein, mouse; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051038:Large-Conductance Calcium-Activated Potassium Channel beta Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D018721:Muscarinic Agonists; D010455:Peptides; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D020033:Protein Isoforms; C064719:iberiotoxin; D002118:Calcium