Serine protease activation of near-silent epithelial Na+ channels

• Published in: American Journal of Physiology: Cell Physiology 2004-01, Vol.286 (1), p.C190-C194
• Main Authors: Caldwell, Ray A, Boucher, Richard C, Stutts, M. Jackson
• Format: Article
• Language: English
• Subjects: 3T3 Cells; Animals; Cell Membrane - metabolism; Epithelial Sodium Channels; Mice; Patch-Clamp Techniques; Rats; Serine Endopeptidases - physiology; Sodium Channels - metabolism; Sodium Channels - physiology; Trypsin - pharmacology
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.00342.2003

The Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina, Chapel Hill, North Carolina 27599-7248 Submitted 6 August 2003 ; accepted in final form 7 September 2003 ABSTRACT 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 ( P o ), 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 -, -, and -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 ( NP o ) < 0.03, where N is the number of channels. Within 1–5 min of 3 µg/ml bath trypsin superfusion, NP o increased 66-fold ( n = 7). In patches observed to contain a single functional channel, trypsin increased P o 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 P o 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. silent channels; protease; epithelial Na + transport; cystic fibrosis; hypertension Address for reprint requests and other correspondence: R. A. Caldwell, Cystic Fibrosis/Pulmonary Research and Treatment Center, CB#7248, Univ. of North Carolina, Chapel Hill, NC 27599-7248 (E-mail: ray_caldwell{at}med.unc.edu ).