Serine protease activation of near-silent epithelial Na+ channels

• Published in: American Journal of Physiology: Cell Physiology 2004, Vol.55 (1), p.C190-C194
• Main Authors: CALDWELL, Ray A, BOUCHER, Richard C, STUTTS, M. Jackson
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Cell membranes. Ionic channels. Membrane pores; Cell structures and functions; Cells; Cystic fibrosis; Enzymes; Fundamental and applied biological sciences. Psychology; Hypertension; Molecular and cellular biology; Sodium
• ISSN: 0363-6143; 1522-1563

The regulation of epithelial Na+ channel (ENaC) function is critical for normal salt and water balance. This regulation is achieved through cell surface insertion/retrieval of channels, by changes in channel open probability (Po), or through a combination of these processes. Epithelium-derived serine proteases, including channel activating protease (CAP) and prostasin, regulate epithelial Na+ transport, but the molecular mechanism is unknown. We tested the hypothesis that extracellular serine proteases activate a near-silent ENaC population resident in the plasma membrane. Single-channel events were recorded in outside-out patches from fibroblasts (NIH/3T3) stably expressing rat alpha-, beta-, and gamma-subunits (rENaC), before and during exposure to trypsin, a serine protease homologous to CAP and prostasin. Under baseline conditions, near-silent patches were defined as having rENaC activity (NPo) < 0.03, where N is the number of channels. Within 1-5 min of 3 micro g/ml bath trypsin superfusion, NPo increased 66-fold (n = 7). In patches observed to contain a single functional channel, trypsin increased Po from 0.02 +/- 0.01 to 0.57 +/- 0.03 (n = 3, mean +/- SE), resulting from the combination of an increased channel open time and decreased channel closed time. Catalytic activity was required for activation of near-silent ENaC. Channel conductance and the Na+/Li+ current ratio with trypsin were similar to control values. Modulation of ENaC Po by endogenous epithelial serine proteases is a potentially important regulator of epithelial Na+ transport, distinct from the regulation achieved by hormone-induced plasma membrane insertion of channels. [PUBLICATION ABSTRACT]