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MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS

Influence of K-Cl cotransporter activity on activation of volume-sensitive Cl^– channels in human osteoblasts

¹Department of Applied Physiology and ²Institute of Orthopedic Research and Biomechanics, University of Ulm, 89081 Ulm, Germany

Submitted 24 June 2002 ; accepted in final form 10 January 2003

The whole cell recording mode of the patch-clamp technique was used to study the effect of hypotonic NaCl or isotonic high-KCl solution on membrane currents in a human osteoblast-like cell line, C1. Both hypotonic NaCl or isotonic high-KCl solution activated Cl^– channels expressed in these cells as described previously. The reversal potential of the induced Cl^– current is more negative when activated through hypotonic NaCl solution (–47 ± 5 mV; n = 6) compared with activation through isotonic high-KCl solution (–35 ± 3 mV; n = 8). This difference can be explained by an increase in intracellular [Cl^–] through the activity of a K-Cl cotransporter. Potassium aspartate was unable to activate the current, and furosemide or DIOA suppressed the increase in Cl^– current induced by isotonic high-KCl solution. In addition, we used the polymerase chain reaction to demonstrate the presence of KCC1–KCC4 mRNA in the osteoblast-like cell line. From these results, we conclude that human osteoblasts express functional K-Cl cotransporters in their cell membrane that seem to be able to induce the indirect activation of volume-sensitive Cl^– channels by KCl through an increase in the intracellular ion concentration followed by water influx and cell swelling.

potasium-chloride cotransporter; KCC1–KCC4; chloride channels; extracellular potassium concentration buffering

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