Stimulation of calcium uptake by parathyroid hormone in renal brush-border membrane vesicles. Relationship to membrane phosphorylation.

The effect of parathyroid hormone (PTH) on Ca2+ uptake was studied in brush-border membrane vesicles (BBMV) prepared from the kidneys of dogs administered 4-5 micrograms/kg of bovine PTH 1-84 in vivo. PTH stimulated Ca2+ uptake at 20 s of incubation from control values of 231 +/- 21 to 306 +/- 30 pmol/mg of protein, p less than 0.001. The stimulation of Ca2+ uptake by PTH was not reversed by incubation of the BBMV with the Ca2+ ionophore, despite the fact that Ca2+ uptake was several times greater than the expected uptake at equilibrium, indicating that most of the uptake represented Ca2+ binding to the BBMV. In BBMV from kidneys exposed to PTH, hypotonic lysis or increasing the osmolality of the solution external to the BBMV did not affect Ca2+ uptake. These data also indicated that the largest fraction of Ca2+ uptake in the presence of a chemical potential represented binding of Ca2+ to BBMV. Ca2+ binding was initially to the exterior of the BBMV, then translocated within the membrane and to the interior vesicular face as assessed by chelation of Ca2+ bound to the BBMV by ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. Incubation of BBMV from kidneys exposed to PTH with gentamicin, which competes with Ca2+ for anionic phospholipid-binding sites, reversed the stimulatory effects of PTH on Ca2+ uptake. Phosphorylation of BBMV and PTH treatment in vivo had similar effects on BBMV phospholipid composition increasing the levels of anionic phospholipids. Phosphorylation of the BBMV also produced gentamicin-inhibitable increases in membrane Ca2+ binding. Phosphorylation of BBMV from kidneys exposed to PTH was inhibited suggesting a higher state of phosphorylation in vivo. The data demonstrate that PTH administered in vivo stimulated Ca2+ binding in BBMV that was gentamicin inhibitable and associated with an increase in the membrane content of anionic phospholipids.