Commitment to differentiation of murine erythroleukemia cells involves a modulated plasma membrane depolarization through Ca2+‐activated K+ channels

Publisher Website
Google Scholar
Abstract
The role of the plasma membrane potential (Δψp) in the commitment to differentiation of murine erythroleukemia (MEL) cells has been studied by analyzing the ionic basis and the time course of this potential in the absence or the presence of different types of inducers. Δψp was determined by measuring the distribution of tetraphenylphosphonium (TPP+) across the plasma membrane and displayed a 22-hour depolarization phase (from −28 to +5 mV) triggered by factors contained in foetal calf serum (FCS) and followed by a nearly symmetrical repolarization phase. After measuring the electrochemical equilibrium potential of Na+, K+, and Cl−, the relative contribution of these ions to Δψp was evaluated by means of ion substitution experiments and by the addition of ion flux inhibitors (tetrodotoxin [TTX], 4-acetoamide-4′-isothiocyanostilbene-2,2′-disulfonate [SITS]) and ionophores (Valinomycin, A23187). The Na+ contribution to Δψp appeared negligible, the potential being essentially generated by K+ and Cl− fluxes. When evaluated by a new mathematical approach, the effects of Valinomycin and A23187 at different times of incubation provided evidence that both the depolarization and the repolarization phase were due to variations of the K+ permeability across the plasma membrane (Pk) mediated by Ca2+-activated K+ channels. All the inducers tested (dimethylsulfoxide [DMSO], hexamethylen-bis-acetamide [HMBA], diazepam), although they did not modify the ionic basis of Δψp, strongly attenuated the depolarization rate of this potential. This attenuation was not brought about when the inducers were added to noninducible MEL cell clonal sublines. Cell commitment occurred only during the depolarization phase and increased proportionally to the attenuation of this phase up to a threshold beyond which the further increase of the attenuation was associated with the inhibition of commitment. The major role of the inducers apparently consisted of the stabilization of the Ca2+-activated K+ channels, suggesting that a properly modulated Δψp depolarization through these channels is primarily involved in the signal generation for MEL cell commitment to differentiation.