Abstract FR549: Deletion of NaX (Scn7a) Channel Does Not Attenuate Central NaCl- or DOCA-Salt-Induced Hypertension in Rats

Increases in extracellular NaCl elevate sympathetic nerve activity and arterial blood pressure (ABP) via specialized NaCl-sensing neurons in circumventricular organs. The NaX (Scn7a) channel is the putative Na + sensor in mice; however, mice have a higher osmotic set point and plasma Na + than rats and humans. Therefore, we tested the extent to which the NaX channel contributes to NaCl-dependent hypertension using a novel NaX KO rat generated by CRISPR/Cas9 deletion of 8,613bp spanning exons 2 through 7 of the Scn7a gene. Scn7a deletion was confirmed by sequencing and absence of mRNA expression in the brain using RNAscope. In the first set of rats, we assessed ABP in wild-type (WT: 2M, 4F) and Sc7a -/- (KO: 4M, 1F) littermates in response to DOCA-salt hypertension produced by uni-nephrectomy, access to 0.9% saline, and silastic deoxycorticosterone acetate pellet (33 mg/100g, SC). There were no differences between strains in baseline ABP (WT: 109±4 vs . KO: 111±2 mmHg), heart rate (WT: 402±10 vs . KO: 402±7 bpm) or saline intake (WT: 17±2 vs . KO: 13±2 mL/100g BW). DOCA treatment significantly raised ABP in both groups; surprisingly, ABP was significantly higher in Sc7a -/- vs . WT rats (175±6 vs . 158±3 mmHg; p<0.01) despite no differences in saline intake between strains (WT: 62±8 vs . KO: 60±8 mL/100g BW). Depressor responses to the ganglionic blocker hexamethonium (30mg/kg, IV) were similar between strains on Day 0 (WT: -54±5 vs . KO: -66±3 mmHg) but enhanced on Day 21 (WT: -77±7 vs . KO: -100±4 mmHg; p < 0.05). There were no differences in plasma or cerebrospinal fluid Na + or Cl - after DOCA treatment. A second group of WT and Scn7a -/- littermates (6-8M, 6-8F per group) received intracerebroventricular infusion (10uL/10min) of 0.15M, 0.3M, or 0.6M NaCl. Central infusion of NaCl produced concentration-dependent increases in ABP of all rats. However, there were no significant differences in the pressor responses between strains at 0.3 M (AUC WT: 184±34 vs . KO: 189±30 mmHg) or 0.6 M NaCl (AUC WT: 266±25 vs . KO: 283±24 mmHg). These results suggest that NaX deletion does not prevent acute or chronic salt-dependent hypertension in rats and may not represent the putative Na + sensor within the hypothalamus. Supported by NIH HL145875 and HL163906