title: Dietary K+ regulates apical membrane expression of maxi-K channels in rabbit cortical collecting duct.
abstract: The cortical collecting duct (CCD) is a final site for regulation of K(+) homeostasis. CCD K(+) secretion is determined by the electrochemical gradient and apical permeability to K(+). Conducting secretory K(+) (SK/ROMK) and maxi-K channels are present in the apical membrane of the CCD, the former in principal cells and the latter in both principal and intercalated cells. Whereas SK channels mediate baseline K(+) secretion, maxi-K channels appear to participate in flow-stimulated K(+) secretion. Chronic dietary K(+) loading enhances the CCD K(+) secretory capacity due, in part, to an increase in SK channel density (Palmer et al., J Gen Physiol 104: 693-710, 1994). Long-term exposure of Ambystoma tigrinum to elevated K(+) increases renal K(+) excretion due to an increase in apical maxi-K channel density in their CDs (Stoner and Viggiano, J Membr Biol 162: 107-116, 1998). The purpose of the present study was to test whether K(+) adaptation in the mammalian CCD is associated with upregulation of maxi-K channel expression. New Zealand White rabbits were fed a low (LK), control (CK), or high (HK) K(+) diet for 10-14 days. Real-time PCR quantitation of message encoding maxi-K alpha- and beta(2-4)-subunits in single CCDs from HK animals was greater than that detected in CK and LK animals (P < 0.05); beta(1)-subunit was not detected in any CCD sample but was present in whole kidney. Indirect immunofluorescence microscopy revealed a predominantly intracellular distribution of alpha-subunits in LK kidneys. In contrast, robust apical labeling was detected primarily in alpha-intercalated cells in HK kidneys. In summary, K(+) adaptation is associated with an increase in steady-state abundance of maxi-K channel subunit-specific mRNAs and immunodetectable apical alpha-subunit, the latter observation consistent with redistribution from an intracellular pool to the plasma membrane.
authors.affiliation: Renal-Electrolyte Division, Dept. of Medicine, Univ. of Pittsburgh, A919 Scaife Hall, 3550 Terrace St., Pittsburgh, PA 15261, USA.
authors.forename: Fadi
authors.initials: F
authors.lastname: Najjar
authors.forename: Hao
authors.initials: H
authors.lastname: Zhou
authors.forename: Tetsuji
authors.initials: T
authors.lastname: Morimoto
authors.forename: James B
authors.initials: JB
authors.lastname: Bruns
authors.forename: Hai-Sheng
authors.initials: HS
authors.lastname: Li
authors.forename: Wen
authors.initials: W
authors.lastname: Liu
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Kleyman
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Satlin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D002412:Cations / Q000378:metabolism; D017931:DNA Primers; D004032:Diet; D004573:Electrolytes / Q000097:blood / Q000652:urine; D005260:Female; D005455:Fluorescent Antibody Technique; D015870:Gene Expression / Q000187:drug effects; D017506:H(+)-K(+)-Exchanging ATPase / Q000378:metabolism; D066298:In Vitro Techniques; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D018613:Microscopy, Confocal; D024681:Potassium Channels, Calcium-Activated / Q000096:biosynthesis* / Q000235:genetics; D017419:Potassium, Dietary / Q000494:pharmacology*; D012333:RNA, Messenger / Q000096:biosynthesis; D011817:Rabbits; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D002412:Cations; D017931:DNA Primers; D004573:Electrolytes; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D017419:Potassium, Dietary; D012333:RNA, Messenger; D017506:H(+)-K(+)-Exchanging ATPase