Calcium Uptake in Isolated Chick Intestinal Epithelial Cells: Role of β‐glucuronidase and TRPV6

Abstract

We have postulated that calcium influx is mediated by PKA and efflux mediated by PKC (1). In the current work, enterocytes from adult birds lacking PKC(2) responded to 1,25D3 with enhanced 45Ca uptake, relative to controls. The steroid response was blocked by Ab 099 against the 1,25D3‐MARRS receptor, but not by 9A7 against the VDR. Likewise, in freshly isolated enterocytes preincubated with calphostin C, 1,25D3 treatment enhanced 45Ca uptake. Cells treated with 100 nM PMA exhibited rapid extrusion of 45Ca, whereas myo‐inositol was without effect. We have noted that in chick enterocytes cultured for 72 h, there is also a loss of steroid‐stimulated PKC activity(3). Under 72 h culture conditions, 1,25D3 also stimulated 45Ca uptake. In response to a report that ß‐glucuronidase (ßG) activates TRPV 5 in kidney, we determined that enterocytes treated with 1,25D3, PTH or forskolin had elevated release of ßG, and addition of ßG to enterocytes stimulated 45Ca uptake. siRNA against either ßG or TRPV6 inhibited steroid‐stimulated 45Ca uptake. Using confocal microscopy we observed steroid enhanced surface staining of anti‐TRPV6 or anti‐ßG due to 1,25D3. We conclude that PKC does regulate efflux while uptake involves PKA‐mediated release of ßG with subsequent activation of TRPV6.