IONIC MECHANISMS OF CA2-DEPENDENT ELECTROLYTE TRANSPORT ACROSS EQUINESWEAT GLAND EPITHELIUM()

1. The ionic mechanism involved in Ca2+-stimulated electrolyte transpo rt in cultured equine su eat gland epithelial cells was studied using the short-circuit current (I-SC) technique. 2. Microscopy revealed tha t the cultured cells grown on Millipore filters formed polarized monol ayers with tight junctions. Monolayers exhibited a mean transepithelia l resistance of 333.9 +/- 40.4 Omega cm(2). 3. Ca2+-mobilizing agents, A23187 (1 mu M) or thapsigargin (0.01-1 mu m), stimulated I-SC while forskolin exerted little effect on the I-SC. 4. Replacement of externa l Cl- by gluconate significantly reduced the I-SC by 63% when stimulat ed by 0.1 mu m thapsigargin. Residual I-SC could be abolished (> 99%) by elimination of HCO3- from the bathing solution. 5. Basolateral addi tion of bumetanide (0.1 mM), ouabain (0.01 mM) and acetazolamide (45 m u M) and apical addition of methyl isobutyl amiloride (MIA, 1-100 mu M ) all had inhibitory effects on the thapsigargin-stimulated I-SC to va rious extents. 6. Substantial current inhibition could be obtained usi ng 4-,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) and dip henylamine-2-carboxylate (DPC) in a concentration-dependent manner. 7. The K+ channel blocker barium (5 mM) was effective on both sides of t he epithelium with a much larger effect on the basolateral side. 8. Th e inhibitory effects of acetazolamide, amiloride, MIA, DIDS and DPC on the thapsigargin-stimulated I-SC were also observed when a Cl--free s olution was used. 9. The results provide evidence for Ca2+-stimulated HCO3- as well as Cl- secretion by equine sweat gland epithelium.