Modulation of Ca2+ levels in keratinocytes by all-trans retinoic acid.
Human epidermal keratinocytes, that have been growth-arrested by removal of epidermal growth factor from the culture medium, are stimulated to proliferate by all-trans retinoic acid (RA). The same treatment inhibits the onset of differentiated features and reduces cell-substrate adhesion. In the present study we show that the same treatment results in a decrease in total cell-associated Ca2+ as measured by changes in the amount of 45Ca2+ bound to cells at equilibrium following RA treatment and by a decrease in intracellular free Ca2+ levels as measured with the Ca(2+)-sensitive dye, Indo-1. The alterations in Ca2+ levels were evident within an hour after RA treatment, were in the range of 30-35% and occurred over the same RA concentration range that stimulated proliferation (i.e., 0.25-1.0 micrograms/ml). When the extracellular Ca2+ concentration was elevated from the normal level of 0.15-1.4 mM, intracellular free Ca2+ increased by a factor of 2 while total cell-associated Ca2+ increased approximately 6-fold. Even under conditions of high extracellular Ca2+, RA was able to reduce cell-associated and intracellular free Ca2+. These data indicate that RA has the capacity to lower Ca2+ levels in keratinocytes concomitantly with its effects on biological behavior.
Varani
J
J
Department of Pathology, University of Michigan Medical School, Ann Arbor 48109.
Inman
D R
DR
Gibbs
D F
DF
Fligiel
S E
SE
Voorhees
J J
JJ
D002118:Calcium / Q000378:metabolism*; D002448:Cell Adhesion / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D006801:Humans; D007424:Intracellular Fluid / Q000378:metabolism; D015603:Keratinocytes / Q000187:drug effects* / Q000378:metabolism; D013268:Stimulation, Chemical; D014212:Tretinoin / Q000494:pharmacology*
D014212:Tretinoin; D002118:Calcium