scholarly journals Absence of Small Conductance K+Channel (SK) Activity in Apical Membranes of Thick Ascending Limb and Cortical Collecting Duct in ROMK (Bartter's) Knockout Mice

2002 ◽  
Vol 277 (40) ◽  
pp. 37881-37887 ◽  
Author(s):  
Ming Lu ◽  
Tong Wang ◽  
Qingshang Yan ◽  
Xinbo Yang ◽  
Ke Dong ◽  
...  
Keyword(s):  
Knockout Mice ◽  
Collecting Duct ◽  
K Channel ◽  
Thick Ascending Limb ◽  
Cortical Collecting Duct ◽  
Apical Membranes ◽  
Small Conductance

Arachidonic acid inhibits activity of cloned renal K+ channel, ROMK1

1996 ◽  
Vol 271 (3) ◽  
pp. F588-F594 ◽  
Author(s):  
C. M. Macica ◽  
Y. Yang ◽  
S. C. Hebert ◽  
W. H. Wang
Keyword(s):  
Arachidonic Acid ◽  
Membrane Fluidity ◽  
Collecting Duct ◽  
K Channel ◽  
Thick Ascending Limb ◽  
Cortical Collecting Duct ◽  
Channel Activity ◽  
Lipoxygenase Inhibitor ◽  
Open Probability ◽  
Apical Membranes

Arachidonic acid (AA) has been shown to inhibit the activity of the low-conductance ATP-sensitive K+ channel in the apical membrane of the cortical collecting duct [W. Wang, A. Cassola, and G. Giebisch. Am. J. Physiol. 262 (Renal Fluid Electrolyte Physiol. 31): F554-F559, 1992]. ROMK1, a K+ channel derived from the rat renal outer medulla, shares many biophysical properties of the native low-conductance K+ channel, which is localized to the apical membranes of the cortical collecting duct and thick ascending limb. This study was designed to determine whether the ROMK channel maintains the property of AA sensitivity of the native low-conductance K+ channel. Experiments were conducted in Xenopus oocytes injected with cRNA encoding the ROMK1 channel by use of patch-clamp techniques. We have confirmed previous reports that the cloned ROMK1 has similar channel kinetics, high open probability, and inward slope conductance as the native low-conductance K+ channel, respectively. Addition of 5 microM AA to an inside-out patch resulted in reversible inhibition of channel activity at a concentration similar to the inhibitor constant for AA on the native K+ channel. The effect of AA on channel activity was preserved in the presence of 10 microM indomethacin, a cyclooxygenase inhibitor, 4 microM cinnamyl-3,4-dihydroxycyanocinnamate, a lipoxygenase inhibitor, and 4 microM 17-octadecynoic acid, an inhibitor of cytochrome P-450 monooxygenases, thus indicating that the effect of AA was not mediated by metabolites of AA. The effect did not appear to be the result of changes in membrane fluidity, since 5 microM eicosatetraynoic acid, an AA analogue that is a potent modulator of membrane fluidity, had no effect. Furthermore, the addition of AA to the outside of the patch also had no effect on channel activity. These results indicate that, like the native low-conductance channel, AA is able to directly inhibit ROMK1 channel activity.

Cloning and localization of a double-pore K channel, KCNK1: exclusive expression in distal nephron segments

1997 ◽  
Vol 273 (4) ◽  
pp. F663-F666 ◽  
Author(s):  
Marcelo Orias ◽  
Heino Velázquez ◽  
Freeman Tung ◽  
George Lee ◽  
Gary V. Desir
Keyword(s):  
Amino Acid ◽  
Collecting Duct ◽  
Human Kidney ◽  
Distal Tubule ◽  
Amino Acid Identity ◽  
Northern Analysis ◽  
K Channel ◽  
Thick Ascending Limb ◽  
Cortical Collecting Duct ◽  
K Channels

The K-selective channel, TOK1, recently identified in yeast, displays the unusual structural feature of having two putative pore regions, in contrast to all previously cloned K channels. Using the TOK1 pore regions as probes, we identified a human kidney cDNA encoding a 337-amino acid protein (hKCNK1) with four transmembrane segments and two pore regions containing the signature sequence of K channels. Amino acid identity to TOK1 is only 15% overall but 40% at the pores. Northern analysis indicates high expression of a 1.9-kb message in brain > kidney >> heart. Nephron segment localization, carried out in rabbit by reverse transcription-polymerase chain reaction, reveals that KCNK1 is expressed in cortical thick ascending limb, connecting tubule, and cortical collecting duct. It was not detected in the proximal tubule, medullary thick ascending limb, distal convoluted tubule, and glomerulus. We conclude that KCNK1 is a unique, double-pore, mammalian K channel, distantly related to the yeast channel TOK1, that is expressed in distal tubule and is a candidate to participate in renal K homeostasis.

Mineralocorticoids decrease the activity of the apical small-conductance K channel in the cortical collecting duct

2005 ◽  
Vol 289 (5) ◽  
pp. F1065-F1071 ◽  
Author(s):  
Yuan Wei ◽  
Elisa Babilonia ◽  
Hyacinth Sterling ◽  
Yan Jin ◽  
Wen-Hui Wang
Keyword(s):  
Protein Tyrosine Kinase ◽  
Collecting Duct ◽  
K Channel ◽  
Sk Channels ◽  
Cortical Collecting Duct ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Herbimycin A ◽  
Sk Channel ◽  
Small Conductance

We used the patch-clamp technique to examine the effect of DOCA treatment (2 mg/kg) on the apical small-conductance K (SK) channels, epithelial Na channels (ENaC), and the basolateral 18-pS K channels in the cortical collecting duct (CCD). Treatment of rats with DOCA for 6 days significantly decreased the plasma K from 3.8 to 3.1 meq and reduced the activity of the SK channel, defined as NPo, from 1.3 in the CCD of control rats to 0.6. In contrast, DOCA treatment significantly increased ENaC activity from 0.01 to 0.53 and the basolateral 18-pS K channel activity from 0.67 to 1.63. Moreover, Western blot analysis revealed that DOCA treatment significantly increased the expression of the nonreceptor type of protein tyrosine kinase (PTK), cSrc, and the tyrosine phosphorylation of ROMK in the renal cortex and outer medulla. The possibility that decreases in apical SK channel activity induced by DOCA treatment were the result of stimulation of PTK activity was further supported by experiments in which inhibition of PTK with herbimycin A significantly increased NPo from 0.6 to 2.1 in the CCD from rats receiving DOCA. Also, when rats were fed a high-K (10%) diet, DOCA treatment did not increase the expression of c-Src and decrease the activity of the SK channel in the CCD. We conclude that DOCA treatment decreased the apical SK channel activity in rats on a normal-K diet and that an increase in PTK expression may be responsible for decreased channel activity in the CCD from DOCA-treated rats.

The Protein Tyrosine Kinase-Dependent Pathway Mediates the Effect of K Intake on Renal K Secretion

Physiology ◽  
2005 ◽  
Vol 20 (2) ◽  
pp. 140-146 ◽  
Author(s):  
Dao-Hong Lin ◽  
Hyacinth Sterling ◽  
Wen-Hui Wang
Keyword(s):  
Tyrosine Kinase ◽  
Tyrosine Phosphorylation ◽  
Protein Tyrosine Kinase ◽  
Collecting Duct ◽  
K Channel ◽  
Thick Ascending Limb ◽  
Cortical Collecting Duct ◽  
Protein Tyrosine ◽  
K Secretion ◽  
Dependent Pathway

Dietary K intake plays an important role in the regulation of K secretion: a decrease stimulates and an increase suppresses kidney expression of protein tyrosine kinase (PTK), which plays a role in regulating Kir1.1 (ROMK), which is responsible for K secretion in the cortical collecting duct (CCD) and K recycling in the thick ascending limb. Tyrosine phosphorylation of ROMK channels increases with low dietary K and decreases with high dietary K. Moreover, stimulation of tyrosine phosphorylation of ROMK1 enhances ROMK1 internalization and reduces the K channel number in the cell surface in the CCD.

High-conductance K+ channel in apical membranes of principal cells cultured from rabbit renal cortical collecting duct anlagen

1987 ◽  
Vol 408 (3) ◽  
pp. 282-290 ◽  
Author(s):  
Alfred H. Gitter ◽  
Klaus W. Beyenbach ◽  
Chadwick W. Christine ◽  
Peter Gross ◽  
Will W. Minuth ◽  
...  
Keyword(s):  
Collecting Duct ◽  
K Channel ◽  
Cortical Collecting Duct ◽  
Principal Cells ◽  
Apical Membranes ◽  
Cells Cultured ◽  
High Conductance

scholarly journals Flow-dependent K+ secretion in the cortical collecting duct is mediated by a maxi-K channel

2001 ◽  
Vol 280 (5) ◽  
pp. F786-F793 ◽  
Author(s):  
Craig B. Woda ◽  
Alvina Bragin ◽  
Thomas R. Kleyman ◽  
Lisa M. Satlin
Keyword(s):  
Collecting Duct ◽  
K Channel ◽  
Sk Channels ◽  
Cortical Collecting Duct ◽  
Flow Rates ◽  
K Secretion ◽  
Tubular Flow ◽  
Flow Stimulation ◽  
Small Conductance

K+ secretion by the cortical collecting duct (CCD) is stimulated at high flow rates. Patch-clamp analysis has identified a small-conductance secretory K+ (SK) and a high-conductance Ca2+-activated K+ (maxi-K) channel in the apical membrane of the CCD. The SK channel, encoded by ROMK, is believed to mediate baseline K+ secretion. The role of the stretch- and Ca2+-activated maxi-K channel is still uncertain. The purpose of this study was to identify the K+ channel mediating flow-dependent K+ secretion in the CCD. Segments isolated from New Zealand White rabbits were microperfused in the absence and presence of luminal tetraethylammonium (TEA) or charybdotoxin, both inhibitors of maxi-K but not SK channels, or apamin, an inhibitor of small-conductance maxi-K+ channels. Net K+ secretion and Na+ absorption were measured at varying flow rates. In the absence of TEA, net K+ secretion increased from 8.3 ± 1.0 to 23.4 ± 4.7 pmol · min−1 · mm−1( P < 0.03) as the tubular flow rate was increased from 0.5 to 6 nl · min−1 · mm−1. Flow stimulation of net K+ secretion was blocked by luminal TEA (8.2 ± 1.2 vs. 9.9 ± 2.7 pmol · min−1 · mm−1 at 0.6 and 6 nl · min−1 · mm−1 flow rates, respectively) or charybdotoxin (6.8 ± 1.6 vs. 8.3 ± 1.6 pmol · min−1 · mm−1 at 1 and 4 nl · min−1 · mm−1 flow rates, respectively) but not by apamin. These results suggest that flow-dependent K+ secretion is mediated by a maxi-K channel, whereas baseline K+ secretion occurs through a TEA- and charybdotoxin-insensitive SK (ROMK) channel.

scholarly journals Hydrolyzable ATP and PIP2 Modulate the Small-conductance K+ Channel in Apical Membranes of Rat Cortical-Collecting Duct (CCD)

2002 ◽  
Vol 120 (5) ◽  
pp. 603-615 ◽  
Author(s):  
Ming Lu ◽  
Steven C. Hebert ◽  
Gerhard Giebisch
Keyword(s):  
Kinase Inhibitors ◽  
Collecting Duct ◽  
K Channel ◽  
Sk Channels ◽  
Cortical Collecting Duct ◽  
Channel Activity ◽  
Sk Channel ◽  
Phosphoinositide Kinase ◽  
Excised Patches ◽  
Small Conductance

The small-conductance K+ channel (SK) in the apical membrane of the cortical-collecting duct (CCD) is regulated by adenosine triphosphate (ATP) and phosphorylation-dephosphorylation processes. When expressed in Xenopus oocytes, ROMK, a cloned K+ channel similar to the native SK channel, can be stimulated by phosphatidylinositol bisphosphate (PIP2), which is produced by phosphoinositide kinases from phosphatidylinositol. However, the effects of PIP2 on SK channel activity are not known. In the present study, we investigated the mechanism by which hydrolyzable ATP prevented run-down of SK channel activity in excised apical patches of principal cells from rat CCD. Channel run-down was significantly delayed by pretreatment with hydrolyzable Mg-ATP, but ATPγS and AMP-PNP had no effect. Addition of alkaline phosphatase also resulted in loss of channel activity. After run-down, SK channel activity rapidly increased upon addition of PIP2. Exposure of inside-out patches to phosphoinositide kinase inhibitors (LY294002, quercetin or wortmannin) decreased channel activity by 74% in the presence of Mg-ATP. PIP2 added to excised patches reactivated SK channels in the presence of these phosphoinositide kinase inhibitors. The protein kinase A inhibitor, PKI, reduced channel activity by 36% in the presence of Mg-ATP. PIP2 was also shown to modulate the inhibitory effects of extracellular and cytosolic ATP. We conclude that both ATP-dependent formation of PIP2 through membrane-bound phosphoinositide kinases and phosphorylation of SK by PKA play important roles in modulating SK channel activity.

scholarly journals Extracellular Atp Inhibits the Small-Conductance K Channel on the Apical Membrane of the Cortical Collecting Duct from Mouse Kidney

2000 ◽  
Vol 116 (2) ◽  
pp. 299-310 ◽  
Author(s):  
Ming Lu ◽  
Gordon G. MacGregor ◽  
Wenhui Wang ◽  
Gerhard Giebisch
Keyword(s):  
Protein Kinase ◽  
Apical Membrane ◽  
Purinergic Receptor ◽  
Collecting Duct ◽  
Extracellular Atp ◽  
K Channel ◽  
Cortical Collecting Duct ◽  
Channel Activity ◽  
Inhibitory Effects ◽  
Small Conductance

We have used the patch-clamp technique to study the effects of changing extracellular ATP concentration on the activity of the small-conductance potassium channel (SK) on the apical membrane of the mouse cortical collecting duct. In cell-attached patches, the channel conductance and kinetics were similar to its rat homologue. Addition of ATP to the bathing solution of split-open single cortical collecting ducts inhibited SK activity. The inhibition of the channel by ATP was reversible, concentration dependent (Ki = 64 μM), and could be completely prevented by pretreatment with suramin, a specific purinergic receptor (P2) blocker. Ranking of the inhibitory potency of several nucleotides showed strong inhibition by ATP, UTP, and ATP-γ-S, whereas α, β-Me ATP, and 2-Mes ATP failed to affect channel activity. This nucleotide sensitivity is consistent with P2Y2 purinergic receptors mediating the inhibition of SK by ATP. Single channel analysis further demonstrated that the inhibitory effects of ATP could be elicited through activation of apical receptors. Moreover, the observation that fluoride mimicked the inhibitory action of ATP suggests the activation of G proteins during purinergic receptor stimulation. Channel inhibition by ATP was not affected by blocking phospholipase C and protein kinase C. However, whereas cAMP prevented channel blocking by ATP, blocking protein kinase A failed to abolish the inhibitory effects of ATP. The reduction of K channel activity by ATP could be prevented by okadaic acid, an inhibitor of protein phosphatases, and KT5823, an agent that blocks protein kinase G. Moreover, the effect of ATP was mimicked by cGMP and blocked by L-NAME (NG-nitro-l-arginine methyl ester). We conclude that the inhibitory effect of ATP on the apical K channel is mediated by stimulation of P2Y2 receptors and results from increasing dephosphorylation by enhancing PKG-sensitive phosphatase activity.

Involvement of actin cytoskeleton in modulation of apical K channel activity in rat collecting duct

1994 ◽  
Vol 267 (4) ◽  
pp. F592-F598 ◽  
Author(s):  
W. H. Wang ◽  
A. Cassola ◽  
G. Giebisch
Keyword(s):  
Actin Cytoskeleton ◽  
Actin Filaments ◽  
Cytochalasin B ◽  
Collecting Duct ◽  
K Channel ◽  
Cortical Collecting Duct ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Channel Inhibition ◽  
Inside Out

We have employed the patch-clamp technique to investigate the role of the actin cytoskeleton in the modulation of the low-conductance K+ channel in the apical membrane of the rat cortical collecting duct (CCD). This K+ channel is inactivated by application of cytochalasin B or D, both compounds known to disrupt actin filaments. The effect of both cytochalasins, B and D, was fully reversible in cell-attached patches, but channel activity could not be fully restored in excised membrane patches. The effect of cytochalasins on channel activity was specific and resulted from depolymerization of the actin cytoskeleton, since application of 10 microM chaetoglobosin C, a cytochalasin analogue that does not depolymerize the actin filaments, had no effect on channel activity in inside-out patches. Addition of either actin monomers or of the polymerizing actin filaments in inside-out patches to the cytosolic medium had no effect on channel activity. This suggests that cytochalasin B- or D-induced inactivation of apical K+ channels is not caused by obstruction of the channel pore by actin. We also observed that channel inhibition by cytochalasin B or D could be blocked by pretreatment with 5 microM phalloidin, a compound that stabilizes actin filaments. We conclude that apical K+ channel activity depends critically on the integrity of the actin cytoskeleton.

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