Rapid action of 1,25-dihydroxyvitamin D3 on hepatocyte phospholipids.
Recent studies have reported cellular effects of 1,25-dihydroxyvitamin D3 within 15 minutes, a time period too rapid to be mediated by nuclear activation. The vitamin increases hepatocyte cytosolic calcium levels in the absence of extracellular calcium within 5 minutes. Since metabolites of phosphatidylinositol have been implicated as second messengers in the regulation of cytosolic calcium, we examined the effect of 1,25-dihydroxyvitamin D3 on hepatocyte phosphatidylinositol turnover and compared these effects to those produced by vasopressin. In isolated hepatocytes labeled with [3H]inositol, 1,25-dihydroxyvitamin D3 (4 nM) increased [3H]glycerophosphorylinositol by 16% (p less than 0.01) within 2.5 minutes, by 18% (p less than 0.01) after 5 minutes, and by 11% (p less than 0.05) after 10 minutes. At a concentration of 20 nM, 1,25-dihydroxyvitamin D3 increased [3H]glycerophosphorylinositol by 27% (p less than 0.01) after 5 minutes. Vitamin D did not affect [3H]inositol polyphosphates. Conversely, vasopressin had no effect on [3H]glycerophosphorylinositol but significantly increased [3H]inositol phosphate, [3H]inositol bisphosphate, and [3H]inositol triphosphate. 1,25-Dihydroxyvitamin D3 (4 nM) decreased [3H]phosphatidylinositol by 10% (p less than 0.05) after 5 minutes and by 16% (p less than 0.01) after 10 minutes. At a concentration of 20 nM, 1,25-dihydroxyvitamin D decreased [3H]phosphatidylinositol by 18% (p less than 0.01) after 5 minutes. The vitamin did not affect [3H]phosphatidylinositol bisphosphate or [3H]phosphatidylinositol trisphosphate. 24,25-Dihydroxyvitamin D had no effect on inositol phospholipids. The effects of 1,25-dihydroxyvitamin D3 on inositol phospholipids were blocked by quinacrine. Bromophenacylbromide inhibited the effects of 1,25-dihydroxyvitamin D3 on inositol phospholipids and also blocked the vitamin-induced increments in cytosolic calcium.(ABSTRACT TRUNCATED AT 250 WORDS)
Baran
D T
DT
Department of Orthopedics, University of Massachusetts Medical Center, Worcester.
Sorensen
A M
AM
Honeyman
T W
TW
D000818:Animals; D002117:Calcitriol / Q000494:pharmacology*; D002118:Calcium / Q000032:analysis; D002852:Chromatography, Ion Exchange; D004951:Esterification; D066298:In Vitro Techniques; D007526:Isoelectric Point; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D010716:Phosphatidylinositols / Q000378:metabolism*; D010740:Phospholipases / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012995:Solubility; D014667:Vasopressins / Q000494:pharmacology
D010716:Phosphatidylinositols; D014667:Vasopressins; D010740:Phospholipases; D010741:Phospholipases A; D002117:Calcitriol; D002118:Calcium