AJP - Endocrinology and Metabolism, Vol 260, Issue 5 E751-E755, Copyright © 1991 by American Physiological Society
Insulin stimulates sodium-dependent phosphate transport by osteoblast-like cells
K. J. Kunkler, L. M. Everett, D. K. Breedlove and S. A. Kempson
Department of Physiology and Biophysics, Indiana University School of Medicine, Indianapolis 46202-5120.
The rat osteosarcoma cell line UMR-106-01 has an osteoblast-like phenotype.
When grown in monolayer culture, these cells transport Pi via a
Na(+)-dependent carrier. The Na(+)-Pi cotransport system is stimulated by
parathyroid hormone (PTH). Because there are insulin receptors on
osteoblast-like cells, we determined possible effects of insulin on
Na(+)-Pi cotransport in UMR-106-01 cells. Incubation of cells with 10(-8) M
insulin for 3 h produced a 73% increase (P less than 0.025) in Na(+)-Pi
cotransport. There was no significant change in Na(+)-L-alanine cotransport
or in Na(+)-independent uptake of Pi and alanine. The stimulatory action of
insulin on Na(+)-Pi cotransport was present within 2 h and was dose
dependent in the range 10(-10) to 10(-7) M. The increase in Na(+)-Pi
cotransport was accompanied by an increase in apparent maximal velocity
with no change in apparent Michaelis constant for Pi. Use of cycloheximide
to block de novo protein synthesis did not interfere with this action of
insulin. We conclude that insulin, like PTH, directly stimulates the
Na(+)-Pi cotransport system in osteoblast-like cells. The mechanism remains
to be determined.
