Biomedical subjects
Publications and source records attributed to Judith Blaine.
The renal regulation of phosphate is a complex process. Clinical disorders of phosphate handling have led to the identification of several genes and proteins involved in the maintenance of phosphate homeostasis. Further work is required to elucidate the precise pathways that regulate renal phosphate transport.
The renal electrogenic Na(+)-HCO3- cotransporter (hkNBCe1) plays a major role in the bicarbonate reabsorption by the kidney. We examined how PMA- and ANG II-activated PKCs regulate hkNBCe1 expressed with or without the ANG II receptors AT(1B) in Xenopus laevis oocytes. We found that 10 nM PMA halved the hkNBCe1 current detected in voltage-clamped oocytes. A PKC-specific inhibitor GF-109203X, and a specific inhibitor of Ca-dependent conventional PKCalphabetagamma, GO-6976, significantly reduced PMA inhibition. PMA did not alter surface expression of the cotransporters, but it significantly increased hkNBCe1-PKCalphabetagamma membrane association. We found that at 10(-6) M, ANG II halved the hkNBCe1 current detected in oocytes coexpressing cotransporters with AT(1B). A PKC-specific inhibitor GF-109203X, and a PKCepsilon translocation inhibitor epsilonV1-2 peptide as well as BAPTA-AM (but not GO-6976), significantly reduced ANG II inhibition. At 10(-6) M, ANG II significantly decreased surface expression of the cotransporters and increased hkNBCe1-PKCepsilon membrane association. Additionally, we found that at 10(-11) and 10(-10) M ANG II stimulated hkNBCe1 current. This effect was blocked by BAPTA-AM and partially reduced by GF-109203X. We also found that ANG II increased intracellular Ca2+ in fluo 4-loaded oocytes. Our results suggest that 1) PMA inhibition of hkNBCe1 is mediated by Ca-dependent PKCalphabetagamma and 10 nM PMA does not induce downregulation of cotransporter surface expression. 2) ANG II (10(-6) M) inhibition of hkNBCe1 is mediated by both Ca-independent PKCepsilon and downregulation of cotransporter surface expression, possibly triggered by intracellular Ca2+ mobilization. 3) Similar to proximal tubule, acute ANG II has a biphasic effect on hkNBCe1 coexpressed with AT(1B) in X. laevis oocytes.