Enhanced sensitivity of NKCC2 to β‐adrenergic receptor stimulation in TALs from Dahl salt sensitive (DSS) rats

Abstract

Abnormally enhanced NKCC2 activity and trafficking in the thick ascending limb (TAL) are related to hypertension in DSS rats. In vivo, DSS rats exhibit higher renal sympathetic nerve activity than Dahl salt resistant (DSR) and greater sympathetic‐induced renal Na reabsorption. In Sprague Dawley rats, β‐adrenergic receptor (β‐AR) stimulation enhances surface NKCC2 levels via cAMP and PKA. We hypothesized that the response to β‐AR stimulation is enhanced in DSS rats prior to the development of hypertension resulting in higher surface NKCC2 expression in TALs. We obtained TALs from DSS and DSR rats fed normal salt and measured surface NKCC2 and cAMP. The β‐AR agonist isoproterenol (ISO, 1μM) slightly enhanced surface NKCC2 in DSR (13 ± 9%), but significantly enhanced it in DSS rats (70 ± 24 %, p<0.05). We next studied if this difference was due to higher cAMP production. ISO‐stimulated cAMP production was similar in TALs from DSS and DSR rats (DSR: 106 ± 22, DSS: 143 ± 18 % increase from baseline). To test whether the higher response to ISO in DSS was due to enhanced cAMP‐induced signaling we measured cAMP‐stimulated NKCC2 phosphorylation at Ser126. db‐cAMP (25 μM) stimulated Ser126 phosphorylation in DSS from 1.2 ± 0.3 to 10.5 ± 3.5 a.u, and from 0.6 ± 0.3 to 1.9 ± 0.6 a.u in DSR TALs (p<0.05). We concluded that β‐AR stimulation of NKCC2 trafficking is enhanced in TALs from DSS rats by a mechanism that may involve enhanced cAMP signaling.