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Figure 10.2 Cell volume and intracellular osmolyte concentration during exposure to hypotonic bath solutions in whole cell patch clamp experiments. If a cell is exposed to a hypotonic solution, water enters the cell and induces a change in cell volume, dVjdt (A). This increase is reflected by the initial change in volume (B, solid line). During the experiment, solutes will enter the cell from the patch pipette, which in turn induces additional water entry. Therefore, the cell volume will increase continuously (B). The intracellular osmolyte concentration, cj (dotted line), decreases rapidly and reaches a stationary constant value while the volume is constantly increasing. See text for details.

where the constant kd describes the rate of diffusion of solutes from pipette to cell and ci and cp reflect the global concentrations of solutes in the cell and in the pipette, respectively. Thus, hypotonic cell swelling in the whole cell patch clamp mode can be described by a system oftwo differential equations with the variables ci and V. Figure 10.2 shows a numerical solution of this system of differential equations. The initial slope of the volume change mainly reflects the influx of water across the plasma membrane, which is faster than the solute exchange via the patch pipette. The subsequent nearly linear increase in volume is a consequence ofthe exchange ofsolutes via the patch pipette. Importantly, this model predicts that ci decreases significantly during an osmotic challenge and reaches a plateau value, despite the continuous increase in cell volume. For further details, see Nilius (2004) and Voets etal. (1999).

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