title: BK-{beta}1 subunit: immunolocalization in the mammalian connecting tubule and its role in the kaliuretic response to volume expansion.
abstract: Large, Ca(2+)-activated K(+) channels (BK), comprised of alpha- and beta-subunits, mediate K(+) secretion during high flow rates in distal nephron segments. Because the BK-beta1 subunit enhances Ca(2+) sensitivity of BK in a variety of cells, we determined its role in flow-induced K(+) secretion and its localization in the mammalian nephron. To determine the role of BK-beta1 in the kaliuretic response to volume expansion, the rate of K(+) excretion (U(K)V) vs. varied urinary flow rates were determined in wild-type and BK-beta1 knockout mice (BK-beta1(-/-)). When flow rate was varied by volume expansion (2 ml.h(-1).25 g body wt(-1)) for 30 to 60 min in wild-type mice, we found that the U(K)V increased significantly with increasing urine flow rates (r(2) = 0.50, P < 0.00001, n = 31), as demonstrated previously in distal nephron of rats and rabbits. However, in BK-beta1(-/-) mice, U(K)V did not vary with changing flow rates (r(2) = 0.15, P = 0.08, n = 20). Using immunohistochemical techniques, we found that BK-beta1 was strongly expressed in the apical membrane of the murine distal nephron and that 98% of BK-beta1 protein detected by histochemistry colocalized with NCX, a marker of connecting tubules (CNT). Both BK-beta1 and NCX colocalized with BK-alpha in separate experiments. Furthermore, we confirmed BK-beta1 protein expression in the apical membrane of connecting tubules in rabbits. BK-beta1 RNA from rabbit CNT was sequenced and was identical to previously published rabbit muscle sequences. These data show that the BK-beta1 accessory subunit is present in the CNT segment of the mammalian distal nephron and has a significant role in the kaliuretic response to increased urinary flow induced by volume expansion.
authors.affiliation: Dept. of Cellular and Integrative Physiology, Univ. of Nebraska Medical Center, Omaha, NE 68198-5850, USA.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Pluznick
authors.forename: Peilin
authors.initials: P
authors.lastname: Wei
authors.forename: P Richard
authors.initials: PR
authors.lastname: Grimm
authors.forename: Steven C
authors.initials: SC
authors.lastname: Sansom
mesh_terms: D000818:Animals; D005260:Female; D007150:Immunohistochemistry; D007685:Kidney Tubules, Collecting / Q000502:physiology*; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009399:Nephrons / Q000502:physiology; D011188:Potassium / Q000652:urine*; D024681:Potassium Channels, Calcium-Activated / Q000235:genetics* / Q000378:metabolism*; D011817:Rabbits
chemical_list: D051036:Large-Conductance Calcium-Activated Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D011188:Potassium