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Original Article

Ion Transport in an Immortalized Rat Submandibular Cell Line SMG-C6

Robert Castro^*,1, Lornell Barlow-Walden^*, Trudi Woodson^*, Jay D. Kerecman, Guo H. Zhang^* and J. Ricardo Martinez

^* Department of Pediatrics, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78284–7812;
Department of Pediatrics, Wilford Hall Medical Center, San Antonio, Texas 78236–5000; and
National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland 20892–2190

The immortalized rat submandibular epithelial cell line, SMG-C6, cultured on porous tissue culture supports, forms polarized, tight-junction epithelia facilitating bioelectric characterization in Ussing chambers. The SMG-C6 epithelia generated transepithelial resistances of 956±84.cm² and potential differences (PD) of -16.9 ± 1.5mV (apical surface negative) with a basal short-circuit current (I_sc) of 23.9 ± 1.7 µA/cm² (n = 69). P2 nucleotide receptor agonists, ATP or UTP, applied apically or basolaterally induced a transient increase in I_sc, followed by a sustained decreased below baseline value. The peak I_sc increase was partly sensitive to Cl^- and K⁺ channel inhibitors, DPC, glibenclamide, and tetraethylammonium (TEA) and was completely abolished following Ca²⁺ chelation with BAPTA or bilateral substitution of gluconate for Cl^-. The major component of basal I_sc was sensitive to apical Na⁺ replacement or amiloride (half-maximal inhibitory concentration 392 nM). Following pretreatment with amiloride, ATP induced a significantly greater I_sc; however, the poststimulatory decline was abolished, suggesting an ATP-induced inhibition of amiloride-sensitive Na⁺ transport. Consistent with the ion transport properties found in Ussing chambers, SMG-C6 cells express the rat epithelial Na⁺ channel -subunit (-rENaC). Thus, cultured SMG-C6 cells produce tight polarized epithelia on permeable support with stimulated Cl^- secretory conductance and an inward I_sc accounted for by amiloride-sensitive Na⁺ absorption.