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1Department Physiology of Biophysics, Weill Medical College of Cornell University, New York, New York 10021; and and 2Institut de Pharmacologie et de Toxicologie, Université de Lausanne, 1005 Lausanne, Switzerland
Submitted 13 January 2003 ; accepted in final form 23 March 2003
Currents through epithelial Na channels (ENaCs) were measured in the
cortical collecting tubule (CCT) of mice expressing truncated 
-subunits
of ENaC, reproducing one of the mutations found in human patients with
Liddle's syndrome. Tubules were isolated from mice homozygous for the Liddle
mutation (L/L) and from wild-type (WT) littermates. Amiloride-sensitive
currents (INa) from single cells were recorded under whole
cell clamp conditions. CCTs from mice kept under control conditions and fed a
diet with normal levels of Na had very small INas (WT: 18
± 13 pA; L/L: 22 ± 8 pA at Vm = –100 mV) that
were not different in WT and L/L animals. However, the L/L mice had much
larger currents when the animals were fed a low-Na diet (WT: 256 ± 127
pA; L/L: 1,820 ± 330 pA) or infused with aldosterone (WT: 285 ±
63 pA; L/L: 1,600 ± 280 pA). Currents from L/L mice were also larger
when animals were pretreated with a high-K diet but not when the CCTs were
stimulated in vitro with 8-CTP-cAMP. Noise analysis of amiloride-induced
fluctuations in INa showed that single-channel currents at
Vm = 0 mV were slightly smaller in L/L mice (WT: 0.33 pA; L/L: 0.24
pA). This difference could be attributed to a decrease in driving force since
current-voltage analysis indicated that intracellular Na was increased in the
L/L animals. Analysis of spontaneous channel noise indicated that the open
probability was similar in the two genotypes(WT: 0.77; L/L: 0.80). Thus the
increase in whole cell current is attributed to a difference in the density of
conducting channels.
kidney; sodium transport; aldosterone; hypertension; amiloride
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