Steroids and exogenous gamma-ENaC subunit modulate cation channels formed by alpha-ENaC in human B lymphocytes.

Previous studies using whole-cell recording methods suggest that human B lymphocytes express an amiloride-sensitive, sodium-permeable channel. The present studies aim to determine whether this channel has biophysical properties and a molecular structure related to the alpha, beta, and gamma subunits of the epithelial sodium channel (ENaC). Reverse transcriptase polymerase chain reaction and Northern blots showed that human B lymphocytes express messages for both alpha- and beta- but not gamma-ENaC. Western blots showed that both alpha- and beta- but not gamma-ENaC proteins are expressed and strongly reduced by antisense oligonucleotides. Patch clamp experiments demonstrated that lymphocyte sodium channels are not active in cell-attached patches. However, membrane stretch can activate a 21-pS nonselective cation channel. The frequency of observance of this channel was significantly reduced by antisense oligonucleotide against alpha-ENaC but not by antisense oligonucleotide against beta-ENaC, indicating that only the alpha subunit of ENaC is necessary to form stretch-activated cation channels. Aldosterone (1.5 microm) reduced the frequency of observance of 21-pS alpha-ENaC channels and simultaneously induced the appearance of spontaneously active 10-pS channels. Antisense oligonucleotide experiments showed that this 10-pS channel is formed from alpha- and beta-ENaC. After expression of exogenous gamma-ENaC, aldosterone again reduced the frequency of observance of the 21-pS alpha-ENaC channel but induced the appearance of a 5-pS channel, presumably a alphabetagamma-ENaC channel. In the absence of aldosterone, the alpha subunit forms an alpha-cryptic channel that is activated by stretch, and in the presence of aldosterone, beta and alpha subunits together form an active channel that is modulated by aldosterone.