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Sackin H
,
Syn S
,
Palmer LG
,
Choe H
,
Walters DE
.
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The effect of external potassium (K) and cesium (Cs) on the inwardly rectifying K channel ROMK2 (K(ir)1.1b) was studied in Xenopus oocytes. Elevating external K from 1 to 10 mM increased whole-cell outward conductance by a factor of 3.4 +/- 0.4 in 15 min and by a factor of 5.7 +/- 0.9 in 30 min (n = 22). Replacing external Na by Cs blocked inward conductance but increased whole-cell conductance by a factor of 4.5 +/- 0.5 over a period of 40 min (n = 15). In addition to this slow increase in conductance, there was also a small, rapid increase in conductance that occurred as soon as ROMK was exposed to external cesium or 10 mM K. This rapid increase could be explained by the observed increase in ROMK single-channel conductance from 6.4 +/- 0.8 pS to 11.1 +/- 0.8 pS (10 mM K, n = 8) or 11.7 +/- 1.2 pS (Cs, n = 8). There was no effect of either 10 mM K or cesium on the high open probability (P(o) = 0.97 +/- 0.01; n = 12) of ROMK outward currents. In patch-clamp recordings, the number of active channels increased when the K concentration at the outside surface was raised from 1 to 50 mM K. In cell-attached patches, exposure to 50 mM external K produced one or more additional channels in 9/16 patches. No change in channel number was observed in patches continuously exposed to 50 mM external K. Hence, the slow increase in whole-cell conductance is interpreted as activation of pre-existing ROMK channels that had been inactivated by low external K. This type of time-dependent channel activation was not seen with IRK1 (K(ir)2.1) or in ROMK2 mutants in which any one of 6 residues, F129, Q133, E132, V121, L117, or K61, were replaced by their respective IRK1 homologs. These results are consistent with a model in which ROMK can exist in either an activated mode or an inactivated mode. Within the activated mode, individual channels undergo rapid transitions between open and closed states. High (10 mM) external K or Cs stabilizes the activated mode, and low external K stabilizes the inactivated mode. Mutation of a pH-sensing site (ROMK2-K61) prevents transitions from activated to inactivated modes. This is consistent with a direct effect of external K or Cs on the gating of ROMK by internal pH.
Baukrowitz,
Modulation of K+ current by frequency and external [K+]: a tale of two inactivation mechanisms.
1995, Pubmed
Baukrowitz,
Modulation of K+ current by frequency and external [K+]: a tale of two inactivation mechanisms.
1995,
Pubmed
Chepilko,
Permeation and gating properties of a cloned renal K+ channel.
1995,
Pubmed
,
Xenbase
Choe,
Permeation properties of inward-rectifier potassium channels and their molecular determinants.
2000,
Pubmed
,
Xenbase
Choe,
Structural determinants of gating in inward-rectifier K+ channels.
1999,
Pubmed
,
Xenbase
Choe,
A conserved cytoplasmic region of ROMK modulates pH sensitivity, conductance, and gating.
1997,
Pubmed
,
Xenbase
Doi,
Extracellular K+ and intracellular pH allosterically regulate renal Kir1.1 channels.
1996,
Pubmed
,
Xenbase
Doyle,
The structure of the potassium channel: molecular basis of K+ conduction and selectivity.
1998,
Pubmed
Döring,
The epithelial inward rectifier channel Kir7.1 displays unusual K+ permeation properties.
1998,
Pubmed
,
Xenbase
Frindt,
Low-conductance K channels in apical membrane of rat cortical collecting tubule.
1989,
Pubmed
Hagiwara,
The anomalous rectification and cation selectivity of the membrane of a starfish egg cell.
1974,
Pubmed
Horton,
Engineering hybrid genes without the use of restriction enzymes: gene splicing by overlap extension.
1989,
Pubmed
Kubo,
Primary structure and functional expression of a mouse inward rectifier potassium channel.
1993,
Pubmed
,
Xenbase
Leipziger,
PKA site mutations of ROMK2 channels shift the pH dependence to more alkaline values.
2000,
Pubmed
,
Xenbase
Liu,
Dynamic rearrangement of the outer mouth of a K+ channel during gating.
1996,
Pubmed
Lopatin,
[K+] dependence of open-channel conductance in cloned inward rectifier potassium channels (IRK1, Kir2.1).
1996,
Pubmed
,
Xenbase
MacGregor,
Partially active channels produced by PKA site mutation of the cloned renal K+ channel, ROMK2 (kir1.2).
1998,
Pubmed
,
Xenbase
Malnic,
Micropuncture study of distal tubular potassium and sodium transport in rat nephron.
1966,
Pubmed
McNicholas,
Regulation of ROMK1 K+ channel activity involves phosphorylation processes.
1994,
Pubmed
,
Xenbase
McNicholas,
pH-dependent modulation of the cloned renal K+ channel, ROMK.
1998,
Pubmed
,
Xenbase
Ortega-Sáenz,
Collapse of conductance is prevented by a glutamate residue conserved in voltage-dependent K(+) channels.
2000,
Pubmed
Palmer,
Is the secretory K channel in the rat CCT ROMK?
1997,
Pubmed
,
Xenbase
Pardo,
Extracellular K+ specifically modulates a rat brain K+ channel.
1992,
Pubmed
,
Xenbase
Sakmann,
Conductance properties of single inwardly rectifying potassium channels in ventricular cells from guinea-pig heart.
1984,
Pubmed
Schlief,
Modification of C-type inactivating Shaker potassium channels by chloramine-T.
1996,
Pubmed
,
Xenbase
Schulte,
pH gating of ROMK (K(ir)1.1) channels: control by an Arg-Lys-Arg triad disrupted in antenatal Bartter syndrome.
1999,
Pubmed
Tsai,
Intracellular H+ inhibits a cloned rat kidney outer medulla K+ channel expressed in Xenopus oocytes.
1995,
Pubmed
,
Xenbase
Vergani,
Mutations in the pore regions of the yeast K+ channel YKC1 affect gating by extracellular K+.
1998,
Pubmed
,
Xenbase
Wang,
Dual modulation of renal ATP-sensitive K+ channel by protein kinases A and C.
1991,
Pubmed
Xu,
Phosphorylation of the ATP-sensitive, inwardly rectifying K+ channel, ROMK, by cyclic AMP-dependent protein kinase.
1996,
Pubmed
,
Xenbase
Zhou,
Mutations in the pore region of ROMK enhance Ba2+ block.
1996,
Pubmed
,
Xenbase