Volume flows and pressure changes during an action potential in cells ofChara australis

Summary It has been suggested that electro-kinetic coupling may be involved in the mechanism of the action potential and that there should therefore be both consequent volume flows and pressure changes associated with such excitation. In a previous paper, such measurements were reported in cells ofChara australis, from which it is also known that during excitation there is an increase in KCl permeability and an efflux of KCl. In this paper, a number of theoretical analyses have been considered and developed pertaining to such measurements and the time-dependent relationships between apparent measured volume flows, true volume flows and turgor pressure changes in cells in various experimental situations. Such volume flows are quantitatively explained primarily from the frictional coupling of water by both K+ and Cl− ions and to a lesser extent by the local osmotic flow owing to KCl enhancement at the wall-membrane interface of the cell. The measured pressure changes of 12×10−3 to 28×10−3 atm during excitation are also correctly predicted as the result of such a volume outflow from the cell which behaves as a hydraulically leaky elastic cylinder and thereby drops in pressure. These conclusions then indicate that the volume flows and pressure changes measured are the incidental consequences of a change in membrane permeability and do not necessarily imply any electro-kinetic mechanism for the action potential itself.