The amiloride-sensitive epithelial sodium channel (ENaC) localizes to the apical membrane of epithelial cells in distal nephron, playing an important role in regulating whole-body Na
+
homeostasis and blood pressure. We were the first to describe the presence of αENaC in human renal proximal tubule cells (hRPTC). Gene variants in αENaC have been shown to be associated with salt sensitivity of blood pressure
(SS)
. We also verified that the specific gene variant rs4764586 was significantly associated with SS (χ
2
=9.67, P=0.046). In our salt sensitivity clinical study, 11% participants (N=27/240) had a paradoxical increase in blood pressure (BP) (≥7-mm Hg) on a low NaCl diet, defined as inverse salt sensitive (
ISS
) as compared to salt resistant (
SR
, 72%) and salt sensitive (
SS
, 17%). The incidence of the minor allele αENaC rs4764586 in the
ISS
group was 2-fold of that in
SR
or
SS
(
ISS
, 14.8%;
SR
, 7.0%;
SS
, 7.1%). Expression of αENaC protein in urine derived hRPTCs was significantly lower in
ISS
than in
SR
(
ISS
, 0.55±0.01, n=3; SR, 0.97±0.12, n=3; SS, 0.87±0.12, n=3; one-way ANOVA,
ISS
vs
SR
p<0.05), with the lowest in the homozygous variants (HV) of rs4764586 and highest in wild type. The heterozygous variant containing hRPTCs had an intermediate expression of αENaC (WT, 0.94±0.11, n=4; Heterozygous, 0.72±0.11, n=4; HV, 0.53, n=1). ENaC-like channels were demonstrated in hRPTCs using single-channel patch-clamp electrophysiology with a conductance of 10.5±0.7 pS and E
rev
39.2±5.5 mV vs 10.3±0.8 pS in SR and ISS lines, respectively. However, in
ISS
baseline ENaC-like channel activity was too low to be recorded without trypsin in the pipette (Po = open probability), unlike
SR
. In contrast,
ISS
cells demonstrated a higher Po than
SR
cells in response to trypsin both immediately and after 4 minutes of activation, even though the number of channels recorded at 4 min after GigaOhm seal formation was lower in the ISS line compared to
SR
line (4.7±1.7 vs 1.75±0.5, p=0.042 in
SR
vs
ISS
lines). These results suggest that
ISS
phenotype may be related to impaired ENaC activity in the renal proximal tubule. The long-term physiologic consequences of the
ISS
phenotype remain to be determined