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J. Gen. Physiol.,
Volume 112, Number 2, August 1, 1998 97-111
From the * Department of Medicine, and The sensitivity of Department of Physiology, Tulane University School of Medicine, New Orleans,
Louisiana 70112
rat epithelial Na+ channel (rENaC) to osmotically or mechanically induced
changes of membrane tension was investigated in the Xenopus oocyte expression system, using both dual electrode
voltage clamp and cell-attached patch clamp methodologies. ENaC whole-cell currents were insensitive to mechanical cell swelling caused by direct injection of 90 or 180 nl of 100-mM KCl. Similarly, ENaC whole-cell currents were insensitive to osmotic cell swelling caused by a 33% decrease of bathing solution osmolarity. The lack of
an effect of cell swelling on ENaC was independent of the status of the actin cytoskeleton, as ENaC remained insensitive to osmotic and mechanical cell swelling in oocytes pretreated with cytochalasin B for 2-5 h. This apparent insensitivity of ENaC to increased cell volume and changes of membrane tension was also observed at the single channel level in membrane patches subjected to negative or positive pressures of 5 or 10 in. of water. However,
and contrary to the lack of an effect of cell swelling, ENaC currents were inhibited by cell shrinking. A 45-min incubation in a 260-mosmol solution (a 25% increase of solution osmolarity) caused a decrease of ENaC currents (at
100 mV) from 3.42 ± 0.34 to 2.02 ± 0.23 µA (n = 6). This decrease of current with cell shrinking was completely blocked by pretreatment of oocytes with cytochalasin B, indicating that these changes of current are not
likely related to a direct effect of cell shrinking. We conclude that rENaC is not directly mechanosensitive when expressed in a system that can produce a channel with identical properties to those found in native epithelia.
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