CAP2 and trypsin effects on amiloride-sensitive I_Na of WT or HA-NT– and V5-CT–tagged or β-S518C mutant channels in oocytes. WT α-, β-, γ-, or double tagged (HA-NT/V5-CT) and mutant α-, β-S518C, and γ-cRNA (0.3 ng each) ENaC subunits and 1 ng CAP2 cRNA were injected into oocytes. 24 h after injection, two-electrode voltage clamp assays were conducted. Currents measured in the presence and absence of 10 μM amiloride, while clamping the membrane voltage to −100 mV, were digitized and recorded. (A) Stimulation of ENaC WT channels by coexpression of CAP2 and 2 μg/ml of exogenous trypsin (n = 24). (B) CAP2 and trypsin (2 μg/ml) stimulation of ENaC α-, β-, and γ-HA-NT/V5-CT–tagged subunits (n = 18). (C) 1 mM MTSET activation of α-, β-S518C, and γ mutant untagged channels with or without CAP2 (n = 24). (A–C) Batches of oocytes were extracted from four to five different frogs. Results are expressed as the means ± SE. * and **, P < 0.0001, significant difference when CAP2- or trypsin-stimulated I_Na is compared with control basal I_Na. Statistical significance was determined using an unpaired Student's t test.