Inwardly rectifying K+ current and differentiation of human placental cytotrophoblast cells in culture

Ion transport is important for driving nutrient transport across the syncytiotrophoblast and yet is poorly understood. We have examined K+ currents under basal conditions in cultured cytotrophoblast cells, at various stages of differentiation, using the whole cell patch clamp technique. Cytotrophoblast cells were isolated from human term placenta and maintained in culture for up to 3 dais. Cells were studied at four stages of progressive morphological differentiation: (i) mononuclear cells, (ii) mononuclear cells in aggregates, (iii) small multinucleate cells and (iv) large multinucleate syncytiotrophoblast-like cells. In the conditions of m;hole cell recording the only K+ selective current identified in all cell types was a strong inwardly rectifying current which was sensitive to Ba-2+ and Cs+. This current was unaffected by intracellular ATP whereas intracellular GTP gammas caused either run down of the current or activated a linear current. The characteristics of the current described we consistent with these of the inwardly rectifying K+ channel Kir2.1. The inwardly rectifying K+ current was observed in three out of 19 (16 per cent) mononuclear cells, seven out of 21 (33 per cent) mononuclear aggregates, eight out of 21 (38 per cent) small multinucleate cells and 16 out of 19 (84 per cent) large multinucleate cells. This inwardly rectifying K+ current is likely to have an important role in determining net K+ diffusion across the syncytiotrophoblast cell membrane! perhaps increasing in importance as the tells terminally differentiate. (C) 2001 Harcourt Publishers Ltd.