Abstract
Stretch-activated cation (SAC) channels play an essential role in sensing and transducing external mechanical stresses in living cells. However, its molecular identity in mammalian cells is not as yet firmly established. In human epithelial HeLa cells, we found the activity of non-selective cation channel which is delicately sensitive to membrane stretch with a negative pressure for half-maximum activation of around 3 cm-H2O. Also, the whole-cell cation current was augmented by osmotic cell swelling. The Mg2+-sensitive, Ca2+-conducting, stretch-activated cation channel current exhibited the hallmark biophysical and pharmacological features of TRPM7 at both single-channel and whole-cell levels. The endogenous expression of TRPM7 in HeLa was confirmed by RT-PCR and western blotting. Treatment with siRNA targeted against TRPM7 led to abolition of stretch-activated single-channel cation currents and of swelling-activated whole-cell cation currents. When the TRPM7 cDNA was transfected into HEK-293T cells, the robust stretch-activated cation channel current exhibited similar biophysical and pharmacological features of endogenous TRPM7 at both single-channel and whole-cell levels. Suppression of the regulatory volume decrease (RVD) upon a hypotonic challenge was observed by application of siRNA for TRPM7, by elimination of extracellular Ca2+ or by addition of a TRPM7 channel blocker. Thus, it is concluded that TRPM7 is the SAC channel endogenously expressed in human epithelial cells and is involved in volume regulation of the cells by serving as a swelling-induced Ca2+ influx pathway. [J Physiol Sci. 2008;58 Suppl:S9]
