Regulation of sodium transport in M-1 cells

The M-1 cell line, derived from the mouse cortical collecting duct (CCD), is being used as a mammalian model of the CCD to study Na+ transport. The present studies aimed to further define the role of various hormones in affecting Na+ transport in M-1 cells grown in defined media. M-1 cells on permeable support, in serum-free media, developed amiloride-sensitive current 4-5 days after seeding. As expected for the involvement of epithelial Na+ channels, alpha-, beta-, and gamma-subunits of the epithelial Na+ channel were identified by RT-PCR. Either dexamethasone (Dex, 10-100 nM) or aldosterone (Aldo, 10(-6)-10(-7) M) for 24 h stimulated transport. Cells grown in the presence of Aldo and Dex had higher transport than with Dex alone. Spironolactone added to Dex media decreased transport. The acute effects of hormones reported to inhibit Na+ transport in CCD were also examined. Epidermal growth factor, phorbol esters, and increased intracellular Ca2+ with thapsigargin did not alter transport. Arginine vasopressin caused a transient increase in transport (probably Cl- secretion), which was not amiloride sensitive. Also, the protease inhibitor aprotinin decreased Na+ transport; in aprotinin-treated cells, trypsin stimulated transport. This study demonstrates that adrenal steroids (Dex > Aldo) stimulate Na+ transport in M-1 cells. At least part of this response may represent activation of mineralocorticoid receptors based on an additive effect of Dex and Aldo, as well as inhibition by spironolactone. Responses to immediate-acting hormones is limited. However, an endogenous protease activity, which activates Na+ transport, is present in these cells.