All-trans retinoic acid reduces membrane fluidity of human dermal fibroblasts. Assessment by fluorescence redistribution after photobleaching.
All-trans retinoic acid (RA) preserves human dermal fibroblast viability and stimulates proliferation in vitro. These effects are mediated, at least in part, by reducing the extracellular Ca2+ requirement. The same concentrations of RA that reduce the extracellular Ca2+ requirement also interrupt movement of Ca 2+ across the fibroblast plasma membrane. Based on these observations, we have examined the effects of RA on membrane properties that could influence Ca2+ movement. Fibroblasts were labeled with 1-acyl-2-(N-4- nitrobenzo-2-oxa-1,3 diazole)-amino-caproyl phosphatidyl-choline (a fluorescent phospholipid analogue) and examined for fluorescence redistribution after photobleaching (FRAP) with a pulse of intense light as a measure of membrane fluidity. Using this approach, we observed that membrane fluidity was higher when the cells were incubated in medium containing a low (sub-optimal) level of extracellular Ca2+ (0.15 mmol/L) than in a medium containing an optimal concentration (1.4 mmol/L). Treatment of the cells with 3 micromol/L RA reduced membrane fluidity of the cells under both high- and low-Ca2+ conditions. These findings demonstrate that RA has a direct effect on the plasma membrane of human dermal fibroblasts. This provides a possible mechanism for the previously identified inhibition of Ca2+ movement across the membrane of the same cells and for the previously identified protective effects against lysis under low-Ca2+ conditions.
Varani
J
J
Department of Pathology, University of Michigan, Ann Arbor 48109, USA.
Burmeister
W
W
Bleavins
M R
MR
Johnson
K
K
D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D017077:Culture Media, Conditioned; D004817:Epidermis / Q000187:drug effects* / Q000502:physiology; D005347:Fibroblasts / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D008560:Membrane Fluidity / Q000187:drug effects*; D008856:Microscopy, Fluorescence; D010777:Photochemistry; D014212:Tretinoin / Q000494:pharmacology*
D017077:Culture Media, Conditioned; D014212:Tretinoin; D002118:Calcium