Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC318
Regulation of the epithelial sodium channel (ENaC) by norepinephrine in cultured mouse renal collecting duct cells
M. K. Mansley1, M. Bertog1, C. Korbmacher1
1. Institut f
Sodium absorption in the aldosterone-sensitive distal nephron (ASDN) plays an important role in the maintenance of body sodium balance and the long term regulation of arterial blood pressure. This absorption is mediated via the epithelial sodium channel (ENaC) which can be regulated by hormones and other factors . Increased renal sympathetic nerve activity has been shown to decrease renal Na+ excretion. This may be attributed to increased tubular Na+ absorption. Recently, a clinical study has demonstrated that renal denervation significantly reduced blood pressure in patients with resistant hypertension . However, the regulatory role of renal sympathetic innervation in tubular Na+ transport is still unclear. Therefore, we investigated the effects of norepinephrine on ENaC-mediated transepithelial Na+ transport in mCCDcl1 cells, a model of renal collecting duct principal cells. These cells endogenously express ENaC and respond to physiological concentrations of aldosterone and vasopressin [3, 4]. Na+ transport across cells cultured on permeable supports was monitored using Ussing chambers to record equivalent short circuit current (ISC). Data are shown as mean ± SEM. Basal ISC averaged 5.1 ± 0.3 µA cm-2 (n=7) and was inhibited by apical addition of 100 µM amiloride. This indicates that basal ISC can be attributed to electrogenic Na+ absorption via ENaC. Basolateral addition of norepinephrine (10 µM) produced a peak increase in ISC that returned to the baseline value within less than one minute. This was followed by a transient inhibition of the ISC by 1.2 ± 0.1 µA cm-2 (n=7) within ~15 min. Over the subsequent 2.5 h, ISC gradually increased by 2.2 ± 0.5 µA cm-2 above baseline (n=7, p < 0.01, paired Student's t-test). In contrast, ISC did not increase in matched vehicle-treated cells (0.2 ± 0.4 µA cm-2, n=7). The ISC component stimulated by norepinephrine was inhibited by amiloride. Apical application of norepinephrine did not alter ISC. When amiloride application preceded the addition of norepinephrine, only the initial ISC peak remained which may be caused by a transient Cl- secretory response. In the presence of amiloride, norepinephrine failed to elicit the transient inhibition and the sustained increase in ISC. This indicates that the transient inhibitory and the sustained stimulatory response to norepinephrine can be attributed to an inhibition and a stimulation of ENaC activity, respectively. In summary, our data indicate that ENaC activity in mouse collecting duct cells can be modulated in a complex manner by the sympathetic transmitter norepinephrine via basolateral receptors. The sustained stimulatory effect of norepinephrine on ENaC-mediated Na+ absorption in the collecting duct may contribute to the development of some forms of Na+ retention and arterial hypertension.
Where applicable, experiments conform with Society ethical requirements