A TRPM4‐LIKE NON‐SELECTIVE CATION CHANNEL IS EXPRESSED IN SMALL INTESTINAL EPITHELIAL CELLS

We used patch‐clamp techniques to characterize ion channels that are expressed in the apical membrane of small intestinal epithelial IEC6 cells. A nearly silent 23‐pS channel was recorded in cell‐attached patches, which was significantly activated when the intracellular Ca 2+ was elevated by ionomycin. The channel was also strongly activated in excised inside‐out patches when the inner leaflet of the patch membrane exposed to 1 mM Ca 2+ , Change in Cl − gradient across the patch membrane did not affect the reversal potential. In contrast, the replacement of Na + with NMDG + in the patch pipette obviously shifted the reversal potential from 0 to ‐60 mV, which is very close to the equilibrium potential calculated according to the concentration gradient of Na + . However, the replacement of Na + with K + in the patch pipette did not affect the reversal potential. These biophysical properties are similar to those of native and expressed TRPM4 characterized in other types of cells. Recent studies suggest that the melastatin subfamily 4 of transient receptor potential channels (TRPM4) plays an important role in modulating the cell membrane potential. Therefore, we also performed confocal microscopy experiments and found that TRPM4 is expressed in IEC6 cells. These data suggest that a TRPM4‐like nonselective cation channel may regulate the transport function of small intestinal epithelial cells by affecting the membrane potential.