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| PRIMARY STRUCTURE AND FUNCTIONAL-PROPERTIES OF AN EPITHELIAL K-CHANNEL |
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| Author(s): ZHOU H, TATE SS, PALMER LG |
| Source: AMERICAN JOURNAL OF PHYSIOLOGY Volume: 266 Issue: 3 Pages: C809-C824 Part: Part 1 Published: MAR 1994 |
| Times Cited: 112 References: 32 |
| Abstract: Expression cloning in Xenopus oocytes was used to identify a clone for a renal K channel. The clone, named ROMK2, was obtained from a cDNA library constructed in the plasmid vector pSPORT using size-selected poly(A)(+) RNA from whole rat kidney. ROMK2 consists of 1,837 nucleotides, with an open reading frame of 1,116 bases predicted to code for a 372-amino acid peptide. The clone appears to be a splice variant of a recently reported K channel (ROMK1) from rat renal outer medulla (He, K. H., C. G. Nichols, W. J. Lederer, J. Lytton, P. M. Vassilev, M. V. Kanazirska, and S. C. Hebert. Nature Lend. 362: 31-37, 1993). Northern blot analysis indicates that ROMK2 is expressed in renal cortex, medulla, and papilla. Expression in other tissues appears to be much lower. The functional properties of the channel as measured in Xenopus oocytes indicate its close relationship to ROMK1 and more distant relationship to the inward rectifier K channel (IRK1) (Kubo, Y, T. J. Baldwin, Y. N. Jan, and L. Y. Jan. Nature Lend. 362: 127-133, 1993). The inward conductance of the channel is a saturable function of external K, with a half-maximal conductance at <5 mM. The selectivity sequence for ion permeability based on reversal potential measurements was K > Rb > NH4 > Na, Li. The conductance to Rb was only one-half that to K. Extracellular Ba2+ and Cs+ blocked the channel in a voltage-dependent manner. The high sensitivity of Cs+ block to voltage is consistent with the channel's operating as a multi-ion pore. The channel was blocked by high concentrations (100 mu M) of glybenclamide. It did not appear to be blocked by extracellular Na+ or tetraethylammonium ion. Patch-clamp measurements indicated a single-channel conductance of 30 pS in the presence of 110 mM K and high open probability that was weakly dependent on voltage. This channel may be involved in maintaining the membrane potential of renal cells and/or mediating renal K secretion. |
| Document Type: Article |
| Language: English |
Addresses:
1. CORNELL UNIV, COLL MED, DEPT PHYSIOL, NEW YORK, NY 10021 USA
2. CORNELL UNIV, COLL MED, DEPT BIOPHYS & BIOCHEM, NEW YORK, NY 10021 USA |
| Publisher: AMER PHYSIOLOGICAL SOC, 9650 ROCKVILLE PIKE, BETHESDA, MD 20814 |
| Subject Category: Physiology |
| IDS Number: NF859 |
| ISSN: 0002-9513 |
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