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Articles in PresS, published online ahead of print October 16, 2002
Am J Physiol Cell Physiol, 10.1152/ajpcell.00044.2002
Submitted on January 29, 2002
Accepted on October 15, 2002
1 Center for Oral Biology, University of Rochester, Rochester, NY, USA
2 Pharmacology & Physiology, University of Rochester Medical Center, Rochester, NY, USA
* To whom correspondence should be addressed. E-mail: ted_begenisich{at}urmc.rochester.edu.
We used molecular biological and patch clamp techniques to identify the Ca2+-activated K+ channel genes in mouse parotid acinar cells. Two types of K+ channels were activated by intracellular Ca2+ with single channel conductance values of 22 and 140 pS (in 135 mM external K+), consistent with the "intermediate" and "maxi-K" classes of Ca2+-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 and so the smaller conductance channel present in acinar cells is likely derived from the mIK1 gene. We found that parotid acinar cells express a single, uncommon splice-variant of the mSlo gene (GenBank accession number AF465244) and heterologously expressed channels of this Slo variant had a single channel conductance indistinguishable from 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 ßsubunits (Kcnmb1 and Kcnmb4) in parotid tissue. A comparison of the iberiotoxin sensitivity of the native current with that of parotid mSlo expressed with each ß subunit in isolation and measurements of the iberiotoxin sensitivity of currents in cells from ß1 knock-out mice suggest that approximately 50% of the large-conductance Ca2+-activated K+ channels in parotid acinar cells are composed of homotetrameric channel proteins from the parotid variant of the Slo gene and the rest are heteromeric proteins composed of the parotid Slo variant in combination with the ß4 subunit.
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