INDUCTION OF OSTEOPROGENITOR CELL-DIFFERENTIATION IN RAT MARROW STROMA INCREASES MITOCHONDRIAL RETENTION OF RHODAMINE 123 IN STROMAL CELLS

Bone marrow stromal cells contain colony forming cells with the potent ial to differentiate into osteoprogenitor (OPC) cells. OPC-stimulation medium, containing dexamethasone, ascorbate, and beta-glycerophosphat e is widely used to recruit OPCs in culture. Cultures were incubated 2 4 h with rhodamine 123 (Rho), on different days, to examine the effect of the OPC-stimulation medium on the mitochondrial membrane potential of stromal cells. Cultures grown in both ordinary medium (DMEM with 1 5% FCS) and OPC-stimulation medium showed 2 Rho retention peaks on day s 3-4 and 10-11. Between days 5 and 10 there was a drop in Rho retenti on/cell. OPC-stimulation medium increased Rho retention by at least tw ice the amount relative to ordinary medium, and has quadrupled it on d ay 7. Incubation with Rho concentrations above 5.0 mug/ml inhibited th e portion of increased Rho retention which was contributed by the OPC- stimulation medium. Prolonged exposure to 0.1, 1.0, and 1 0.0 mug/ml R ho for 12 days only slightly increased day 12 ALP activity/cell, had n o effect on day-21 mineralization and only the high dose, 1 0.0 mug/ml , doubled stromal cell proliferation. Under 24 h incubation Rho concen trations of 1.0 mug/ml and below can serve as a marker for mitochondri al membrane potential in differentiating stromal cells. The results in dicate that under both culture conditions stromal cell mitochondria un dergo cycles of high and low membrane potential states and that the OP C-stimulation medium constantly maintains an elevated membrane potenti al relative to ordinary medium. (C) 1993 Wiley-Liss, Inc.