Subunits alpha, beta and gamma of the epithelial Na+ channel (ENaC) are functionally related to the hypertonicity-induced cation channel (HICC) in rat hepatocytes
Specific small interfering RNA (siRNA) constructs were used to test for the functional relation of subunits alpha, beta, and gamma of the epithelial Na+ channel (ENaC) to the hypertonicity-induced cation channel (HICC) in confluent rat hepatocytes. In current-clamp recordings, hypertonic stress (300 -> 400 mosM) increased membrane conductance from 75.4 +/- 9.4 to 91.1 +/- 11.2 pS (p<0.001). The effect was completely blocked by 100 mu M amiloride and reduced to 46, 30, and 45% of the control value by anti-alpha-, anti-beta-, and anti-gamma-rENaC siRNA, respectively. Scanning acoustic microscopy revealed an initial shrinkage of cells from 6.98 +/- 0.45 to 6.03 +/- 0.43 pl within 2 min. This passive response was then followed by a regulatory volume increase (RVI) by 0.42 +/- 0.05 pl (p<0.001). With anti-alpha-, anti-beta-, and anti-gamma-rENaC siRNA, the volume response was reduced to 31, 31, and 36% of the reference level, respectively. It is concluded that all three subunits of the ENaC are functionally related to RVI and HICC activation in rat hepatocytes.