Hypertension Resistance Polymorphisms in ROMK Alter Channel Function by Different Mechanisms

Abstract

The ROMK potassium channel plays a critical role in renal sodium handling. Genome sequencing efforts in the Framingham Heart Study cohort recently revealed an association between suspected loss‐of‐function polymorphisms in ROMK and resistance to hypertension, suggesting that ROMK activity is also a determinant of blood pressure in the general population. Here, we examine whether these sequence variants do, in fact, alter ROMK function and explore the mechanisms. As assessed by two‐microelectrode voltage clamp in Xenopus Oocytes, 3/5 of the variants (R193P, H251Y and T313FS) displayed an almost complete attenuation of whole‐cell ROMK channel activity. Surface antibody binding to external epitope tagged channels and analysis of glycosylation‐state maturation revealed that these variants prevent channel expression at the plasmalemma, likely as a consequence of ER retention. The other variants (P166S, R169H) had no obvious effect on the basal channel activity or surface expression but, instead, displayed a regulated‐gating defect. Apparent PIP2 binding affinity of the variants was reduced, causing channels to become susceptible to inhibition by GPCR‐mediated stimulation of PIP2 hydrolysis. In summary, hypertension resistance sequence variants inhibit ROMK channel function by different mechanisms, providing new insights into the role of the channel in blood pressure control.