Modification of membrane parameters and cell differentiation

HT-29 cells are an established cell line of human colon adenocarcinoma. Considering that several transformed cells possess an increased membrane fluidity and cholesterol (Ch) and phospholipids play an important role in the modulations of plasma membrane fluidity we determined some parameters in normal and Ch containing media. The presence of 100 mg/ml Ch causes an initial cell loss and reduces growth rate until confluence. CEA production is much higher in Ch treated cells than in controls during the first four days of colture. The cellular [Na+], and [K+] are in the range of normal enterocytes. In low Na+ experiments there is a great reduction of Vmax, Km is not modified. The unidirectional flux of sugar is linear within 2 seconds. Time-course experiments show a decrease of equilibrium uptake in low Na+ and in ouabain versus controls. Electron microscopy shows that cells grown in Ch tend to collect the microvilli at one pole. Shifting back to a normal medium, the microvilli lose their polar distribution. The membrane potential is higher in Ch grown cells (-23.6 \ub1 1.6 mV vs. -19.6 \ub1 0.9 mV). The lowering of [K+]o results in a hyperpolarization, higher in the presence than in the absence of Ch. The increase of [K+]o leads to a depolarization greater in controls than in the presence of Ch. Ch seems to increase the electrical resistance of the membrane. Amiloride hyperpolarizes the cell only after a long exposure. 10-3 M ouabain depolarizes the cell at lower concentrations, ouabain depolarizes more rapidly the cells grown in normal conditions than those grown in Ch. In conclusion the Ch affect plasma membrane properties and the results seem to indicate an attempt by the cell to differentiate