Potassium secretion by voltage-gated potassium channel Kv1.3 in the rat kidney

Abstract

The fine regulation of Na+and K+transport takes place in the cortical distal nephron. It is well established that K+secretion occurs through apical K+channels: the ROMK and the Ca2+- and voltage-dependent maxi-K. Previously, we identified the voltage-gated Kv1.3 channel in the inner medulla of the rat kidney (Escobar LI, Martínez-Téllez JC, Salas M, Castilla SA, Carrisoza R, Tapia D, Vázquez M, Bargas J, Bolívar JJ. Am J Physiol Cell Physiol 286: C965–C974, 2004). To examine the role of Kv1.3 in the renal regulation of K+homeostasis, we characterized the effect of dietary K+on the molecular and functional expression of this channel. We performed real-time-PCR and immunoblot assays in kidneys from rats fed a control (CK; 1.2% wt/wt) or high-K+(HK; 10% wt/wt) diet for 5–15 days. Kv1.3 mRNA and protein expression did not change with HK in the whole kidney. However, dietary K+loading provoked a change in the cellular distribution of Kv1.3 from the cytoplasm to apical membranes. Immunolocalization of Kv1.3 detected the channel exclusively in the intercalated cells. We investigated whether Kv1.3 mediated K+transport in microperfused cortical collecting ducts (CCDs). The HK diet led to an increase in net K+transport from 7.4 ± 1.1 (CK) to 11.4 ± 1.0 (HK) pmol·min−1·mm−1. Luminal margatoxin, a specific blocker of Kv1.3, decreased net K+secretion in HK CCDs to 6.0 ± 1.6 pmol·min−1·mm−1. Our data provide the first evidence that Kv1.3 channels participate in K+secretion and that apical membrane localization of Kv1.3 is enhanced in the intercalated cells by dietary K+loading.