We have previously reported that TRPV6, and its activating enzyme β-glucuronidase mediate 1,25(OH)2D3-stimulated calcium uptake in isolated chick intestinal epithelial cells. In the current study, we used dose-response analyses for three mediators of calcium uptake, 1,25(OH)2D3, parathyroid hormone (PTH), and forskolin, to compare calcium uptake and enzyme release. For 1,25(OH)2D3, 130 pM-, 300 pM-, 650 pM- and 1200 pM steroid elicited, no increase in calcium uptake, 140% increase, 180% increase and again no increase, respectively, relative to corresponding controls. The same pattern was observed with β-glucuronidase release with 300 pM- or 650 pM 1,25(OH)2D3 eliciting a 170%, and 260% increase relative to corresponding controls, respectively. The peptide bPTH(1-34) was tested at 26 pM-, 65 pM- or 325 pM hormone which also exhibited a biphasic dose-response curve with 65 pM bPTH (1-34) increasing calcium uptake to 180% of controls and β-glucuronidase release to 155% of corresponding controls. Finally, 10 µM forskolin elicited no increase in calcium uptake, while 20 µM and 40 µM agonist increased calcium uptake to 150% of corresponding controls. Similarly, no increase in enzyme release was noted at 10 µM, while 20 µM and 40 µM forskolin resulted in 130% and 125% increase in β-glucuronidase release, respectively, relative to corresponding controls. As a negative control, 100 nM phorbol ester neither increased calcium uptake nor increased β-glucuronidase release, relative to corresponding controls. We conclude that each of the active agonists have closely parallel dose response curves for enhanced β-glucuronidase release, and stimulated calcium uptake.
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