The cell model of the electrolyte transport mechanisms for cultured human colonocytes. Electromotive forces of the cellular pathways

The purpose of this work was to explain the chloride secretory model of the human colonocytes in terms of the equivalent electromotive forces and the relative apical ionic permeabilities using a conventional micro-electrode technique and different ion-substitution experiments. Both equivalent electromotive forces (for apical and basolateral membranes: E_a=−47.7±5.1 mV and E_b=−65.2±2.9 mV, respectively) depend strongly on the external K⁺ concentration. The most important conclusion is that both cell membrane potentials are largely dominated by a K⁺ permeability. The apical membrane has low Na⁺ and Cl⁻ permeabilities in non-stimulated conditions (P_Na/P_K=0.06±0.01 and P_Cl/P_K=0.23±0.09). An interesting response was found for the basolateral Na⁺ substitutions. Lowering the basolateral Na⁺ concentration at 1 mM we have seen a slow, but large depolarisation of the cell membrane potential of about 30 mV. We think that this is mostly caused by the presence of the basolateral Na⁺/H⁺ exchanger mechanism for the intracellular pH regulation. The Na⁺/K⁺ pump has a significant contribution to the basolateral electromotive force. The basolateral membrane has also a Cl⁻ permeability in non-stimulated conditions, but the basolateral Na⁺ permeability is undetectable.