Volume regulation in a toad epithelial cell line: role of coactivation of K+ and Cl- channels.

1. We have measured changes in cell volume, membrane potential and ionic currents in distal nephron A6 cells following a challenge with hypotonic solutions (HTS). 2.

Ca2+ release and activation of K+ and Cl- currents by extracellular ATP in distal nephron epithelial cells.

We have measured ionic currents and changes in intracellular Ca2+ concentration ([Ca2+]i) induced by extracellular ATP in single epithelial cells of the distal nephron from toad (A6 cells). ATP increased [Ca2+]i and concomitantly activated ionic currents. The ATP concentration for half-maximal increase in [Ca2+]i was approximately 10 microM.

Volume-activated chloride currents are not correlated with P-glycoprotein expression.

It has been proposed that P-glycoprotein, the product of the human MDR1 gene, may function not only as a drug transporter but, depending on the conditions, as a volume-activated Cl- channel [Valverde, Diaz, Sepúlveda, Gill, Hyde and Higgins (1992) Nature (London) 355, 830-833; Gill, Hyde, Higgins, Valverde, Mintenig and Sepúlveda (1992) Cell 71, 23-32]. To verify this hypothesis, we have compared volume-activated Cl- currents with the level of MDR1 mRNA and its protein product in the human KB3 (epitheloid lung cancer) and HeLa cell lines. The related MDR2 was also included to find out whether it could account for observed discrepancies between Cl- current and MDR1 expression.

Cytoskeletal modulation of the response to mechanical stimulation in human vascular endothelial cells.

Possible interactions of cytoskeletal elements with mechanically induced membrane currents and Ca2+ signals were studied in human endothelial cells by using a combined patch-clamp and Fura II technique. For mechanical stimulation, cells were exposed to hypotonic solution (HTS). The concomitant cell swelling activates a Cl- current, releases Ca2+ from intracellular stores and activates Ca2+ influx.

Volume-activated Cl- currents in different mammalian non-excitable cell types.

The existence and properties of volume-activated Cl- currents were studied in 15 different cell types (endothelium: human umbilical vein, human aorta, bovine pulmonary artery; fibroblasts: Swiss 3T3, L, C3H 10T1/2 and COS-1; epithelium: KB3, HeLa and A6; blood cells: RBL-2H3 and Jurkat; endothelioma cells derived from both subcutaneous and thymic hemangiomas; skin: IGR1 melanoma). Volume-activated Cl- currents with common characteristics, i.e.