Changes in inositol transport during DMSO-induced differentiation of HL60 cells towards neutrophils

[³H]Inositol uptake by HL60 cells was measured during DMSO-induced differentiation towards neutrophils. The values for K_m (53.2 μM) and V_max (5.3 pmol/min per 10⁶ cells) obtained for control HL60 cells are in good agreement with previously published figures for this cell line. Inositol transport into HL60 cells was an active, saturable and specific process which was unaffected by extracellular glucose concentrations. Inositol transport rates changed during DMSO-induced differentiation of HL60 cells towards neutrophils. An increase in inositol transport rates occurred during the first 4 days of exposure to 0.9% DMSO and was concommitant with the period leading to growth arrest and prior to the acquisition of the differentiated phenotype. These changes preceded the rise in intracellular inositol concentration from 10.9 to 132.7 μM seen between day 1 and day 5. After 4 days exposure to DMSO the rate of inositol transport fell to a value of 3.1 ± 0.3 pmol/min per 10⁶ cells at day 7, this was accompanied by a small reduction in intracellular inositol from a peak value of 132.7 to 112 μM. The inositol transport rate, thus, appears to closely accompany changes in the intracellular concentration of inositol. Inositol transport in human peripheral blood neutrophils was an order of magnitude slower than the value for uninduced HL60 cells, but the K_m for inositol transport was similar in both cell types and was unchanged during HL60 differentiation. This suggests that changes in inositol transport rate are achieved by the modulation of a commonly expressed inositol transporter, one consequence of which is the alteration of intracellular inositol concentrations.