ALL-TRANS-RETINOIC ACID INHIBITS FLUCTUATIONS IN INTRACELLULAR CA2+ RESULTING FROM CHANGES IN EXTRACELLULAR CA2+

Previous studies have shown that all-trans retinoic acid (RA) preserve s fibroblast viability, and stimulates their proliferation, in part, b y reducing the extracellular Ca2+ requirement (Am J Pathol 1990, 130:1 275). Based on this observation, we have in the present study examined the effects of RA on Ca2+ mobilization in human dermal fibroblasts. F or these studies we used the Ca2+-binding dyes, Fluo-3 and Indo-1. Usi ng flurorescence of Fluo-3-loaded cells or Indo-1-loaded cells as indi cators of intracellular free Ca2+, we observed that treatment of the c ells with RA did not, by itself alter the concentration of intracellul ar Ca2+. Nor did it interfere with the rapid, transient rise in intrac ellular Ca2+ induced by treatment with ionomycin However, treatment of the cells with RA prevented re-equilibration of intracellular Ca2+ wh en the cells were initially equilibrated in low Ca2+ (0.15 mmol/L) cul ture medium and then switched to high Ca2+ (1.4 mmol/L;) medium or whe n cells were first equilibrated in high Ca2+ medium and then switched to low Ca2+ medium. This effect of RA could be seen within seconds aft er treatment and the effect tons observed 1 day after treatment (longe st time point examined), The effect was concentration dependent and co ncentrations of RA that modulated Ca2+ re-equilibration (0.3 to 3.0 mu mol/L) were the same as those that have previously been shown to prom ote fibroblast survival and growth. A biologically inactive retinoid d id not have this effect. Specificity of the response was suggested by the finding that concentrations of RA that modulated Ca2+ movement had no effect on Ba2+ transport. These data suggest that RA prevents re-e quilibration of intracellular Ca2+ in human denial fibroblasts by inte rfering with Ca2+ movement across the plasma membrane.