Abstract P199: Gene Variants in Human Renal Proximal Tubule Alpha ENaC are Associated With Inverse Salt Sensitivity of Blood Pressure

Abstract

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