Abstract MP35: Pharmacological Inhibition And Knockout Of K ir 7.1 Does Not Affect The Development Of Salt-Sensitive Hypertension In The Dahl SS Rat

Ion channels play a vital role in the kidney’s ability to maintain electrolyte homeostasis, and mutations of certain inwardly rectifying K + channels (K ir ) have been associated with various tubulopathies that can cause salt-wasting and as a consequence, low blood pressure. K ir 7.1 is a member of the K ir family, that helps maintain resting membrane potential; however, its role in the kidney is not well understood. Immunohistochemistry in the kidney confirmed that K ir 7.1 is expressed in both aquaporin 2 and sodium chloride co-transporter positive cells, suggesting it may affect distal tubule K + handling. We hypothesized that K ir 7.1 is involved in renal K + homeostasis and may influence the development of salt-sensitive (SS) hypertension. To examine the role of K ir 7.1 during the development of SS hypertension, we used both a genetic knockout of the gene encoding K ir 7.1, Kcnj13 , on the Dahl SS background and pharmacological inhibition; SS Kcnj13-/- was lethal and we used SS Kcnj13+/- . Mean arterial pressure (MAP) in response to a high salt diet was determined by telemetry or arterial catheter. In the genetic model, there was no difference in MAP development between wild type and SS Kcnj13+/- rats (153±6 vs. 159±7, mmHg; n=11 for each group) after 3 weeks on a 4% NaCl diet. Additionally, there were no differences in K + or Na + urinary excretion in WT vs. SS Kcnj13+/- . For the pharmacological studies, ML418, a novel and highly specific K ir 7.1 inhibitor, was administered daily by i.v. infusion during 2 weeks of 8% NaCl diet. While no significant differences in MAP or K + excretion were observed between vehicle or drug treated rats, administration of ML418 had significantly increased urinary Na + excretion (197±54 vs. 333±21, Na/Cre, vehicle vs. ML418; n≥3 for each group, p=0.02). Moreover, equivalent short circuit current measurements of polarized mCCD cells demonstrated that K ir 7.1 antagonism by ML418 reduced vectoral Na + transport. Overall, these results indicate that K ir 7.1 can impact renal Na + homeostasis, but loss of basolateral K ir 7.1 conductance is insufficient to alter development of hypertension, likely due to compensation by the primary basolateral K ir ’s in the distal nephron such as K ir 4.1 and K ir 5.1.

Human genotyping and an experimental model reveal NPR-C as a possible contributor to morbidity in coarctation of the aorta

Coarctation of the aorta (CoA) is a common congenital cardiovascular (CV) defect characterized by a stenosis of the descending thoracic aorta. Treatment exists, but many patients develop hypertension (HTN). Identifying the cause of HTN is challenging because of patient variability (e.g., age, follow-up duration, severity) and concurrent CV abnormalities. Our objective was to conduct RNA sequencing of aortic tissue from humans with CoA to identify a candidate gene for mechanistic studies of arterial dysfunction in a rabbit model of CoA devoid of the variability seen with humans. We present the first known evidence of natriuretic peptide receptor C (NPR-C; aka NPR3) downregulation in human aortic sections subjected to high blood pressure (BP) from CoA versus normal BP regions (validated to PCR). These changes in NPR-C, a gene associated with BP and proliferation, were replicated in the rabbit model of CoA. Artery segments from this model were used with human aortic endothelial cells to reveal the functional relevance of altered NPR-C activity. Results showed decreased intracellular calcium ([Ca²⁺]_i) activity to C-type natriuretic peptide (CNP). Normal relaxation induced by CNP and atrial natriuretic peptide was impaired for aortic segments exposed to elevated BP from CoA. Inhibition of NPR-C (M372049) also impaired aortic relaxation and [Ca²⁺]_i activity. Genotyping of NPR-C variants predicted to be damaging revealed that rs146301345 was enriched in our CoA patients, but sample size limited association with HTN. These results may ultimately be used to tailor treatment for CoA based on mechanical stimuli, genotyping, and/or changes in arterial function.