Hormonal regulation of sodium-dependent phosphate transport in opossum kidney cells

There are multiple regulators of renal proximal tubule sodium-dependent pho sphate (Na+-Pi) transport, including 1,25-dihydroxyvitamin D (1,25-Vit. D), parathyroid hormone (PTH), insulin-like growth factor 1 (IGF-1), and arach idonic acid (AA) and/or its metabolites. The purpose of our studies was to determine whether the effect of these factors on Pi transport is synergisti c or antagonistic. The control solution or the substances were added indepe ndently or coincidentally to opossum kidney (OK) cells before incubation fo r 4 h. 1,25-Vit. D (10(-8) M) had no significant effect on Pi transport (up arrow 6.8%; p = 0.8). PTH (10(-7) M) significantly inhibited Pi transport by 39.6% (p < 0.0001). IGF-1 (10(-8) M) stimulated Pi transport by 19.6% (p < 0.0001). The AA metabolite 20-HETE (10(-7) M) had no significant impact o n Pi transport (down arrow6.4; p = 0.3). The combined effect of 1,25-Vit. D and PTH was no different from PTH alone (p = 0.2). Likewise, addition of e ither 1,25-Vit. D or 20-HETE to IGF-1 failed to affect the magnitude of the increase on Pi transport induced by IGF-1 atone (p = 0.4, p = 0.6, respect ively). The combination of 20-HETE and PTH was not different from that obse rved with PTH alone (p = 0.9). We conclude that in OK cells, PTH inhibits w hereas IGF-1 stimulates Pi transport into OK cells. The effects of each of these hormones a re independent and unaffected by either 1,25-Vit. D or 20- HETE. Copyright (C) 2001 S. Karger AG, Basel.