ROMK is required for expression of the 70-pS K channel in the thick ascending limb

2004 ◽  
Vol 286 (3) ◽  
pp. F490-F495 ◽  
Author(s):  
Ming Lu ◽  
Tong Wang ◽  
Qingshang Yan ◽  
Wenhui Wang ◽  
Gerhard Giebisch ◽  
...  
Keyword(s):  
Functional Expression ◽  
Bartter Syndrome ◽  
Salt Transport ◽  
K Channel ◽  
Thick Ascending Limb ◽  
Channel Activity ◽  
Loss Of Function ◽  
High K ◽  
Hypokalemic Alkalosis ◽  
Severe Reduction

Apical potassium recycling is crucial for salt transport by the thick ascending limb (TAL). Loss-of-function mutations in the K channel, ROMK (Kir1.1; KCNJ1), cause Bartter syndrome, a genetically heterogeneous disorder characterized by severe reduction in salt absorption by the TAL, Na wasting, polyuria, and hypokalemic alkalosis. ROMK(-/-) null mice exhibit a Bartter phenotype and lack the small-conductance (30-pS) apical K channel (SK) in the TAL. However, a distinct 70-pS K channel can also significantly contribute to the apical conductance of TAL. We now examine the effect of ROMK deletion on the functional expression of the 70-pS K channel in the TAL. Functional expression of the 70-pS K channel was low [average channel acitivty ( NPo) = 0.02] in ROMK(+/+) mice on a control K diet but increased to 0.27 by high-K intake for 2 wk. In contrast, the high-K diet decreased NPo of SK by ∼30%, from 2.04 to 1.44. In ROMK heterozygous (+/-) mice on a control K diet, SK activity was about one-half of that observed in ROMK(+/+) mice (0.95 vs. 2.04). The high-K diet also reduced SK activity in ROMK(+/-) mice by ∼40% (from 0.95 to 0.55) but increased NPo of the 70-pS K channel from 0 to 0.09 in ROMK(+/-) mice. This corresponds to ∼30% of channel activity ( NPo = 0.27) observed in ROMK(+/+) mice. Neither the 70-pS nor the 30-pS K channels were observed in TAL cells from ROMK(-/-) mice on either the normal or high-K diets. Thus functional expression of the 70-pS K channel is enhanced by increasing dietary K and requires expression of ROMK. It is likely that ROMK forms a critical subunit of the 70-pS K channel, accounting for the loss of apical K secretory channel activity in ROMK Bartter syndrome.

scholarly journals Adult presentation of Bartter syndrome type IV with erythrocytosis

2015 ◽  
Vol 13 (4) ◽  
pp. 604-606 ◽  
Author(s):  
Ita Pfeferman Heilberg ◽  
Cláudia Tótoli ◽  
Joaquim Tomaz Calado
Keyword(s):  
Late Onset ◽  
Bartter Syndrome ◽  
Sodium Reabsorption ◽  
Thick Ascending Limb ◽  
Syndrome Type ◽  
Loss Of Function ◽  
Mild Phenotype ◽  
Type Iv ◽  
Hypokalemic Alkalosis ◽  
A Subunit

Abstract Bartter syndrome comprises a group of rare autosomal-recessive salt-losing disorders with distinct phenotypes, but one unifying pathophysiology consisting of severe reductions of sodium reabsorption caused by mutations in five genes expressed in the thick ascending limb of Henle, coupled with increased urinary excretion of potassium and hydrogen, which leads to hypokalemic alkalosis. Bartter syndrome type IV, caused by loss-of-function mutations in barttin, a subunit of chloride channel CLC-Kb expressed in the kidney and inner ear, usually occurs in the antenatal-neonatal period. We report an unusual case of late onset presentation of Bartter syndrome IV and mild phenotype in a 20 years-old man who had hypokalemia, deafness, secondary hyperparathyroidism and erythrocytosis.

The Role of 20-Hete in Mediating the Effect of Diatary K Intake on the Apical K Channels in the Mtal.

Hypertension ◽  
2000 ◽  
Vol 36 (suppl_1) ◽  
pp. 710-710
Author(s):  
WenHui Wang ◽  
RuiMin Gu ◽  
Yuan Wei ◽  
Michael Balazy ◽  
Houli Jiang
Keyword(s):  
K Channel ◽  
Thick Ascending Limb ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Deficient Diet ◽  
K Channels ◽  
Medullary Thick Ascending Limb ◽  
A Value ◽  
High K

P95 We have used the patch clamp technique to study the effect of dietary-K intake on the apical K channels in the medullary thick ascending limb (mTAL) of rat kidneys. The channel activity, defined by NPo, of the 30 pS and 70 pS K channel was 0.18 and 0.11 in the mTAL from rats on a K-deficient diet, respectively. In contrast, NPo of the 30 pS and the 70 pS K channels increased to 0.60 and 0.80 in the tubules from animals on a high-K diet, respectively. We have also used GC/MC to measure the intracellular production of 20-hydroxyeicosanotetraenoic acid (20-HETE) in the mTAL. The concentration of 20-HETE was 0.8 pg/μg protein in the mTAL from rats on a high-K diet and increased significantly to 4.6 pg/μg protein in the tubules from rats on a K-deficient diet. Addition of N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS) or 17-octadecynoic acid (17ODYA), agents which inhibit the formation of 20-HETE, had no significant effect on the activity of the 30 pS K channels. However, DDMS/17ODYA significantly increased the activity of the apical 70 pS K channel from 0.11 to 0.91 in the mTAL from rats on a K-deficient diet. In contrast, inhibition of the cytochrome P450 metabolism of arachidonic acid (AA) increased NPo from 0.64 to 0.81 in the tubules from animals on a high-K diet. Furthermore, the concentration of 20-HETE required to block the channel activity by 50% was the same in the mTAL from rats on a high K diet as that on a K-deficient diet. This indicates that the diminished response of the 70 pS K channel to the inhibition of P450 metabolism of AA is not the result of decreasing 20-HETE sensitivity in the mTAL from rats on a high K diet. Finally, the pretreatment of the tubules with DDMS increased NPo of the 70 pS K channels in the mTAL from rats on a K-deficient diet to 0.76, a value which is not significantly different from the NPo in the tubules from rats on a high-K diet. We conclude that an increase in 20-HETE production is involved in reducing the activity of the apical 70 pS K channels in the mTAL from rats on a K-deficient diet.

scholarly journals K Depletion Enhances the Extracellular Ca2+-Induced Inhibition of the Apical K Channels in the Mtal of Rat Kidney

2001 ◽  
Vol 119 (1) ◽  
pp. 33-44 ◽  
Author(s):  
Rui-Min Gu ◽  
Yuan Wei ◽  
Ho-Lin Jiang ◽  
Dao-Hong Lin ◽  
Hyacinth Sterling ◽  
...  
Keyword(s):  
Rat Kidney ◽  
Inhibitory Effect ◽  
K Channel ◽  
Thick Ascending Limb ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
No Donor ◽  
P450 Monooxygenase ◽  
High K ◽  
K Depletion

We have shown previously that raising extracellular Ca2+ inhibited the apical 70-pS K channel in the thick ascending limb (TAL; Wang, W.H., M. Lu, and S.C. Hebert. 1996. Am. J. Physiol. 270:C103–C111). We now used the patch-clamp technique to study the effect of increasing the extracellular Ca2+ on the 70-pS K channel in the mTAL from rats on a different K diet. Increasing the extracellular Ca2+ from 10 μM to 0.5, 1, and to 1.5 mM in the mTAL from rats on a K-deficient (KD) diet inhibited the channel activity by 30, 65, and 90%, respectively. In contrast, raising the extracellular Ca2+ to 1.5 mM had no significant effect on channel activity in the mTAL from animals on a high K (HK) diet and further increasing the extracellular Ca2+ to 2.5, 3.5, and 5.5 mM decreased the channel activity by 29, 55, and 90%, respectively. Inhibition of the cytochrome P450 monooxygenase completely abolished the effect of the extracellular Ca2+ on channel activity in the mTAL from rats on a different K diet. In contrast, blocking cyclooxygenase did not significantly alter the responsiveness of the 70-pS K channel to the extracellular Ca2+. Moreover, addition of sodium nitropruside, a nitric oxide (NO) donor, not only increased the channel activity, but also blunted the inhibitory effect of the extracellular Ca2+ on the 70-pS K channel and decreased 20-hydroxyeicosatetraenoic acid (20-HETE) concentration in the mTAL from rats on a KD diet. In contrast, inhibiting NOS with L-NAME enhanced the inhibitory effect of the extracellular Ca2+ on the channel activity and increased 20-HETE concentration in the mTAL from rats on a high K diet. Western blot has further shown that the expression of inducible NO synthase (iNOS) is significantly higher in the renal medulla from rats on an HK diet than that on a KD diet. Also, addition of S-nitroso-N-acetylpenicillamine abolished the inhibitory effect of arachidonic acid on channel activity in the mTAL, whereas it did not block the inhibitory effect of 20-HETE. We conclude that a low dietary K intake increases the sensitivity of the 70-pS K channel to the extracellular Ca2+, and that a decrease in NOS activity is involved in enhancing the inhibitory effect of the extracellular Ca2+ on channel activity in the mTAL during K depletion.

Two types of K+ channel in thick ascending limb of rat kidney

1994 ◽  
Vol 267 (4) ◽  
pp. F599-F605 ◽  
Author(s):  
W. H. Wang
Keyword(s):  
Apical Membrane ◽  
Rat Kidney ◽  
Inhibitory Effect ◽  
K Channel ◽  
Thick Ascending Limb ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
K Channels ◽  
Inside Out

We have used the patch-clamp technique to study the apical K+ channels in the thick ascending limb (TAL) of the rat kidney. Two types of K+ channels, a low-conductance and an intermediate-conductance K+ channel, were identified in both cell-attached and inside-out patches. We confirmed the previously reported intermediate-conductance K+ channel (72 pS), which is inhibited by millimolar cell ATP, acidic pH, Ba2+, and quinidine (4). We now report a second K+ channel in apical membrane of the TAL. The slope conductance of this low-conductance K+ channel is 30 pS, and its open probability is 0.80 in cell-attached patches. This channel is not voltage dependent, and application of 2 mM ATP in the bath inhibits channel activity in inside-out patches. In addition, 250 microM glyburide, an ATP-sensitive K+ channel inhibitor, blocks channel activity, whereas the same concentration of glyburide has no inhibitory effect on the 72-pS K+ channel. Channel activity of the 30-pS K+ channel decreases rapidly upon excision of patches (channel run down). Application of 0.1 mM ATP and the catalytic subunit of adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase A (PKA) restores channel activity. Furthermore, addition of 0.1 mM 8-(4-chlorophenylthio)-cAMP or 50-100 pM vasopressin in the cell-attached patches increases channel activity. In conclusion, two types of K+ channels are present in the apical membrane of TAL of rat kidney, and PKA plays an important role in modulation of the low-conductance K+ channel activity.

Arachidonic acid inhibits K channels in basolateral membrane of the thick ascending limb

2002 ◽  
Vol 283 (3) ◽  
pp. F407-F414 ◽  
Author(s):  
Rui-Min Gu ◽  
Wen-Hui Wang
Keyword(s):  
Arachidonic Acid ◽  
Basolateral Membrane ◽  
Inhibitory Effect ◽  
K Channel ◽  
Thick Ascending Limb ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
K Channels ◽  
Cytochrome P 450

We have used the patch-clamp technique to study the effect of arachidonic acid (AA) on the basolateral K channels in the medullary thick ascending limb (mTAL) of rat kidney. An inwardly rectifying 50-pS K channel was identified in cell-attached and inside-out patches in the basolateral membrane of the mTAL. The channel open probability ( P o) was 0.51 at the spontaneous cell membrane potential and decreased to 0.25 by 30 mV hyperpolarization. The addition of 5 μM AA decreased channel activity, identified as NP o, from 0.58 to 0.08 in cell-attached patches. The effect of AA on the 50-pS K channel was specific because 10 μM cis-11,14,17-eicosatrienoic acid had no significant effect on channel activity. To determine whether the effect of AA was mediated by AA per se or by its metabolites, we examined the effect of AA on channel activity in the presence of indomethacin, an inhibitor of cyclooxygenase, or N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS), an inhibitor of cytochrome P-450 monooxygenase. Inhibition of cyclooxygenase increased channel activity from 0.54 to 0.9. However, indomethacin did not abolish the inhibitory effect of AA on the 50-pS K channel. In contrast, inhibition of cytochrome P-450 metabolism not only increased channel activity from 0.49 to 0.83 but also completely abolished the effect of AA. Moreover, addition of DDMS can reverse the inhibitory effect of AA on channel activity. The notion that the effect of AA was mediated by cytochrome P-450-dependent metabolites of AA is also supported by the observation that addition of 100 nM of 20-hydroxyeicosatetraenoic acid, a main metabolite of AA in the mTAL, can mimic the effect of AA. We conclude that AA inhibits the 50-pS K channel in the basolateral membrane of the mTAL and that the effect of AA is mainly mediated by cytochrome P-450-dependent metabolites of AA.

Dietary K intake regulates the response of apical K channels to adenosine in the thick ascending limb

2004 ◽  
Vol 287 (5) ◽  
pp. F954-F959 ◽  
Author(s):  
Dimin Li ◽  
Yuan Wei ◽  
Wen-Hui Wang
Keyword(s):  
Adenosine Receptor ◽  
K Channel ◽  
Thick Ascending Limb ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Cgs 21680 ◽  
Adenosine Receptor Agonist ◽  
Dependent Pathway ◽  
Adenosine Analog

We used the patch-clamp technique to study the effect of adenosine on the apical 70-pS K channel in the thick ascending limb (TAL) of the rat kidney. Application of 1 μM cyclohexyladenosine (CHA), an adenosine analog, stimulated apical 70-pS K channel activity and increased the product of channel open probability and channel number ( NPo) from 0.34 to 0.7. Also, addition of CGS-21680, a specific A2a adenosine receptor agonist, mimicked the effect of CHA and increased NPo from 0.33 to 0.77. The stimulatory effect of CHA and CGS-21680 was completely blocked by H89, an inhibitor of protein kinase A (PKA), or by inhibition of adenylate cyclase with SQ-22536. This suggests that the stimulatory effect of adenosine analogs is mediated by a PKA-dependent pathway. The effect of adenosine analog was almost absent in the TAL from rats on a K-deficient (KD) diet for 7 days. Application of DDMS, an agent that inhibits cytochrome P-450 hydrolase, not only significantly increased the activity of the 70-pS K channel but also restored the stimulatory effect of CHA on the 70-pS K channel in the TAL from rats on a KD diet. Also, the effect of CHA was absent in the presence of 20-HETE. Inhibition of PKA blocked the stimulatory effect of CHA on the apical 70-pS K channel in the presence of DDMS in the TAL from rats on a KD diet. We conclude that stimulation of adenosine receptor increases the apical 70-pS K channel activity via a PKA-dependent pathway and that the effect of adenosine on the apical 70-pS K channel is suppressed by low-K intake. Moreover, the diminished response to adenosine is the result of increase in 20-HETE formation, which inhibits the cAMP-dependent pathway in the TAL from rats on a KD diet.

Phospholipase A2 is involved in mediating the effect of extracellular Ca2+ on apical K+ channels in rat TAL

1997 ◽  
Vol 273 (3) ◽  
pp. F421-F429 ◽  
Author(s):  
W. Wang ◽  
M. Lu ◽  
M. Balazy ◽  
S. C. Hebert
Keyword(s):  
Phospholipase A2 ◽  
Fluorescent Dyes ◽  
Rat Kidney ◽  
K Channel ◽  
Thick Ascending Limb ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Acetoxymethyl Ester ◽  
K Channels ◽  
Stimulation Of

Raising extracellular Ca2+ (Ca2+o) stimulating the Ca(2+)-sensing receptor (CaR) decreased the activity of the apical 70-pS K+ channel via a cytochrome P-450-dependent mechanism in the thick ascending limb (TAL) of the rat kidney [W. H. Wang, M. Lu, and S. C. Hebert. Am. J. Physiol. 270 (Cell Physiol. 39): C103-C111, 1996]. We have now used the patch-clamp technique and fluorescent dyes to investigate the signaling mechanism by which this effect is produced. Addition of 500 microM gadolinium (Gd3+), an agent which has been shown to activate the CaR (E. M. Brown, G. Gamba, D. Riccardi, M. Lombardi, R. Butters, O. Kifor, A. Sun, M. A. Hediger, J. Lytton, and S. C. Hebert. Nature 366: 575-580, 1993), mimics the inhibitory effect of raising Ca2+o from 1.1 to 5 mM on channel activity. Effects of the high Ca2+o and Gd3+ were abolished by blockade of phospholipase A2 (PLA2) but not by inhibition of phospholipase C (PLC). Raising Ca2+o also increased 20-hydroxyeicosatetraenoic acid production significantly. To investigate the effect of stimulation of the CaR on intracellular Ca2+ (Ca2+i), we used the acetoxymethyl ester of fura 2 to monitor the Ca2+i. Raising Ca2+o from 1.1 to 5 mM increased the Ca2+i significantly from 50 to 150 nM. However, addition of thapsigargin failed to abolish the effect of 5 mM Ca2+o on Ca2+i. Also, application of Gd3+ only slightly increased the Ca2+i, suggesting that elevation of the Ca2+i by high Ca2+o was the result of an influx of Ca2+ rather than enhanced Ca2+ release from Ca2+ stores. That the increase in Ca2+ influx is not mainly responsible for the effect of stimulating the CaR on channel activity is further supported by experiments in which 500 microM Gd3+ inhibited the K+ channel in cell-attached patches in a Ca(2+)-free bath. Furthermore, addition of 500 microM Gd3+ or 5 mM Ca2+o decreased intracellular Na+ measured with fluorescent sodium indicator, suggesting inhibition of Na+ transport. We conclude that PLA2 is involved in the stimulation of the CaR-induced inhibition of apical K+ channels in the TAL.

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.

Adenosine stimulates the basolateral 50 pS K channels in the thick ascending limb of the rat kidney

2007 ◽  
Vol 293 (1) ◽  
pp. F299-F305 ◽  
Author(s):  
Ruimin Gu ◽  
Jing Wang ◽  
Yunhong Zhang ◽  
Wennan Li ◽  
Ying Xu ◽  
...  
Keyword(s):  
Adenosine Receptor ◽  
Rat Kidney ◽  
Basolateral Membrane ◽  
K Channel ◽  
Thick Ascending Limb ◽  
Dependent Manner ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
K Channels ◽  
Adenosine Receptor Agonist

We used the patch-clamp technique to examine the effect of adenosine on the basolateral K channels in the thick ascending limb (TAL) of the rat kidney. A 50-pS inwardly rectifying K channel was detected in the basolateral membrane, and the channel activity was decreased by hyperpolarization. Application of adenosine (10 μM) increased the activity of basolateral 50 pS K channels, defined by NPo, from 0.21 to 0.41. The effect of adenosine on the 50 pS K channels was mimicked by cyclohexyladenosine (CHA), which increased channel activity by a dose-dependent manner. However, inhibition of the A1 adenosine receptor with 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX) failed to block the effect of CHA. In contrast, application of 8-(3-chlorostyryl) caffeine (CSC), an A2 adenosine antagonist, abolished the stimulatory effect of CHA. The possibility that the effect of adenosine and adenosine analog on the basolateral 50 pS K channel was the result of activation of the A2 adenosine receptor was also suggested by the observation that application of CGS-21680, a selected A2A adenosine receptor agonist, increased the channel activity. Also, inhibition of PKA with N-[2-(methylamino)ethyl]-5-isoquinoline sulfonamide-2HC1 abolished the stimulatory effect of CHA on the basolateral 50 pS K channel. Moreover, addition of the membrane-permeable cAMP analog increases the activity of 50 pS K channels. We conclude that adenosine activates the 50 pS K channel in the basolateral membrane of the TAL and the stimulatory effect is mainly mediated by a PKA-dependent pathway via the A2 adenosine receptor in the TAL.

scholarly journals Angiotensin II type 2 receptor regulates ROMK-like K+ channel activity in the renal cortical collecting duct during high dietary K+ adaptation

2014 ◽  
Vol 307 (7) ◽  
pp. F833-F843 ◽  
Author(s):  
Yuan Wei ◽  
Yi Liao ◽  
Beth Zavilowitz ◽  
Jin Ren ◽  
Wen Liu ◽  
...  
Keyword(s):  
Collecting Duct ◽  
No Synthase ◽  
K Channel ◽  
Ang Ii ◽  
Cortical Collecting Duct ◽  
Channel Activity ◽  
High K ◽  
Pka Pathway

The kidney adjusts K+ excretion to match intake in part by regulation of the activity of apical K+ secretory channels, including renal outer medullary K+ (ROMK)-like K+ channels, in the cortical collecting duct (CCD). ANG II inhibits ROMK channels via the ANG II type 1 receptor (AT1R) during dietary K+ restriction. Because AT1Rs and ANG II type 2 receptors (AT2Rs) generally function in an antagonistic manner, we sought to characterize the regulation of ROMK channels by the AT2R. Patch-clamp experiments revealed that ANG II increased ROMK channel activity in CCDs isolated from high-K+ (HK)-fed but not normal K+ (NK)-fed rats. This response was blocked by PD-123319, an AT2R antagonist, but not by losartan, an AT1R antagonist, and was mimicked by the AT2R agonist CGP-42112. Nitric oxide (NO) synthase is present in CCD cells that express ROMK channels. Blockade of NO synthase with N-nitro-l-arginine methyl ester and free NO with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt completely abolished ANG II-stimulated ROMK channel activity. NO enhances the synthesis of cGMP, which inhibits phosphodiesterases (PDEs) that normally degrade cAMP; cAMP increases ROMK channel activity. Pretreatment of CCDs with IBMX, a broad-spectrum PDE inhibitor, or cilostamide, a PDE3 inhibitor, abolished the stimulatory effect of ANG II on ROMK channels. Furthermore, PKA inhibitor peptide, but not an activator of the exchange protein directly activated by cAMP (Epac), also prevented the stimulatory effect of ANG II. We conclude that ANG II acts at the AT2R to stimulate ROMK channel activity in CCDs from HK-fed rats, a response opposite to that mediated by the AT1R in dietary K+-restricted animals, via a NO/cGMP pathway linked to a cAMP-PKA pathway.

Sign in / Sign up

Export Citation Format

Share Document