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Am J Physiol Cell Physiol 284: C535-C546, 2003. First published October 16, 2002; doi:10.1152/ajpcell.00044.2002
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Vol. 284, Issue 2, C535-C546, February 2003

Molecular identification of Ca2+-activated K+ channels in parotid acinar cells

Keith Nehrke1,*, Claire C. Quinn1,*, and Ted Begenisich2

1 Center for Oral Biology, Aab Institute of Biomedical Sciences, and 2 Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York 14642

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; 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.

secretory cells; fluid secretion; single channels; patch clamp

* K. Nehrke and C. C. Quinn contributed equally to this work.




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