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G Giebisch

Publications and source records attributed to G Giebisch.

At least 55 records · Page 3Linked to original sources
PubMed1997

Nitric oxide-induced hyperpolarization stimulates low-conductance Na+ channel of rat CCD.

We used the patch-clamp technique in the split-open cortical collecting duct (CCD) to investigate the effect of nitric oxide (NO) on the low-conductance (6-pS) Na+ channel that can be blocked by 1 microM amiloride. We confirmed that the number of Na+ channels increased significantly in CCDs of rats on a low-Na+ diet (17). Application of 100 microM N(G)-nitro-L-arginine methyl ester (L-NAME), an agent that blocks endogenous NO synthase, reduced NPo [the product of channel number (N) and open probability (Po)] to 45% of the control value. The effect of L-NAME was specific, since addition of D-NAME, which does not inhibit NO synthase, did not change the activity of the Na+ channel. That the effect of L-NAME results from inhibition of NO synthase is further confirmed by experiments in which addition of an exogenous NO donor, either 10 microM S-nitroso-N-acetyl penicillamine or sodium nitroprusside (SNP), restored the Na+ channel activity when it had been blocked by L-NAME. The action of NO involves a guanosine 3',5'-cyclic monophosphate (cGMP)-dependent pathway, since 100 microM 8-bromo-cGMP (8-BrcGMP) mimicked the effect of SNAP on K+ channels. However, 100 microM 8-BrcGMP did not alter the activity of Na+ channels in inside-out patches, suggesting an indirect action. Because the Na+ channel is activated by hyperpolarization (19) and NO stimulates basolateral K+ channels (16), we tested whether hyperpolarization mediated the effect of NO. In perforated whole cell recordings, addition of L-NAME depolarized the cell membrane from -73 to 51 mV, and application of 10 microM SNP repolarized the membrane to -68 mV. Furthermore, the L-NAME-induced decrease in NPo was effectively restored by 25 mV hyperpolarization of the patch membranes, and addition of 2 mM Ba2+ also abolished the effect of L-NAME. We concluded that the stimulatory effect of NO on the Na+ channel is an indirect effect mediated by a NO-induced increase of basolateral K+ conductance.

Animals↗
PubMed1997

Mechanisms of chloride transport in the proximal tubule.

The major fraction of filtered Cl- is reabsorbed in the proximal tubule. An important component of Cl- reabsorption is passive and paracellular, driven by the lumen-negative potential difference in the early proximal tubule and the outwardly directed concentration gradient for Cl- in the later proximal tubule. Evidence suggests that a significant additional component of NaCl reabsorption in the proximal tubule is active and transcellular. Cl-/formate and Cl-/oxalate exchangers have been identified as mechanisms of uphill Cl- entry across the apical membrane. For steady-state Cl- absorption to occur by these mechanisms, formate and oxalate must recycle from lumen to cell. Recent studies indicate that recycling of formate occurs by H(+)-coupled formate transport in parallel with Na+/H+ exchange, whereas oxalate recycling takes place by oxalate/sulfate exchange in parallel with Na(+)-sulfate cotransport. The predominant route for Cl- exit across the basolateral membrane is via Cl- channels. Unresolved issues include the adequacy of formate recycling to sustain Cl- absorption by Cl-/formate exchange, the existence and contributions of additional mechanisms for apical Cl entry and basolateral Cl- exit, and the relative magnitudes of transcellular and paracellular transport under physiological conditions. In addition, the molecular identification and mechanisms of regulation of the Cl-/formate and Cl-/oxalate exchangers remain to be defined.

Animals↗
PubMed1997

A functional CFTR-NBF1 is required for ROMK2-CFTR interaction.

In a previous study on inside-out patches of Xenopus oocytes, we demonstrated that the cystic fibrosis transmembrane conductance regulator (CFTR) enhances the glibenclamide sensitivity of a coexpressed inwardly rectifying K+ channel, ROMK2 (C. M. McNicholas, W. B. Guggino, E. M. Schwiebert, S. C. Hebert, G. Giebisch, and M. E. Egan. Proc. Natl. Acad. Sci. USA 93: 8083-8088, 1996). In the present study, we used the two-microelectrode voltage-clamp technique to measure whole cell K+ currents in Xenopus oocytes, and we further characterized the enhanced sensitivity of ROMK2 to glibenclamide by CFTR. Glibenclamide inhibited K+ currents by 56% in oocytes expressing both ROMK2 and CFTR but only 11% in oocytes expressing ROMK2 alone. To examine the role of the first nucleotide binding fold (NBF1) of CFTR in the ROMK2-CFTR interaction, we studied the glibenclamide sensitivity of ROMK2 when coexpressed with CFTR constructs containing mutations in or around the NBF1 domain. In oocytes coinjected with ROMK2 and a truncated construct of CFTR with an intact NBF1 (CFTR-K593X), glibenclamide inhibited K+ currents by 46%. However, in oocytes coinjected with ROMK2 and a CFTR mutant truncated immediately before NBF1 (CFTR-K370X), glibenclamide inhibited K+ currents by 12%. Also, oocytes expressing both ROMK2 and CFTR mutants with naturally occurring NBF1 point mutations, CFTR-G551D or CFTR-A455E, display glibenclamide-inhibitable K+ currents of only 14 and 25%, respectively. Because CFTR mutations that alter the NBF1 domain reduce the glibenclamide sensitivity of the coexpressed ROMK2 channel, we conclude that the NBF1 motif is necessary for the CFTR-ROMK2 interaction that confers sulfonylurea sensitivity.

Amino Acid Substitution↗
PubMed1996

Role of NHE3 in mediating renal brush border Na+-H+ exchange. Adaptation to metabolic acidosis.

The aims of the present study were to estimate the fraction of renal brush border membrane Na+-H+ exchange activity mediated by the isoform NHE3 and to evaluate whether the increased brush border Na+-H+ exchange observed in metabolic acidosis is due to increased expression of NHE3 protein. Compared with other isoforms, NHE3 is known to have a unique profile of sensitivity to pharmacologic inhibitors, including relative resistance to amiloride analogs and HOE694. We therefore assessed the inhibitor sensitivity of pH gradient-stimulated 22Na uptake in renal brush border vesicles isolated from normal rats. The I50 values for amiloride (30 microM), dimethylamiloride (10 microM), ethylisopropylamiloride (6 microM), and HOE694 (>100 microM) were markedly dissimilar from those reported for NHE1 and NHE2 but were nearly identical to reported values for NHE3. Na+-H+ exchange activity in renal brush border vesicles isolated from rats with 5 days of NH4Cl-induced metabolic acidosis was increased 1.5-fold compared with control rats, with no change in inhibitor sensitivity. Western blot analysis indicated that NHE3 protein expression was greater in brush border membranes from acidotic compared with control rats. We conclude that virtually all measured Na+-H+ exchange activity in brush border membranes from control and acidotic rats is mediated by NHE3 and that metabolic acidosis causes increased expression of renal brush border NHE3 protein.

Acidosis↗
PubMed1996

Sensitivity of a renal K+ channel (ROMK2) to the inhibitory sulfonylurea compound glibenclamide is enhanced by coexpression with the ATP-binding cassette transporter cystic fibrosis transmembrane regulator.

We demonstrate here that coexpression of ROMK2, an inwardly rectifying ATP-sensitive renal K+ channel (IKATP) with cystic fibrosis transmembrane regulator (CFTR) significantly enhances the sensitivity of ROMK2 to the sulfonylurea compound glibenclamide. When expressed alone, ROMK2 is relatively insensitive to glibenclamide. The interaction between ROMK2, CFTR, and glibenclamide is modulated by altering the phosphorylation state of either ROMK2, CFTR, or an associated protein, as exogenous MgATP and the catalytic subunit of protein kinase A significantly attenuate the inhibitory effect of glibenclamide on ROMK2. Thus CFTR, which has been demonstrated to interact with both Na+ and Cl- channels in airway epithelium, modulates the function of renal ROMK2 K+ channels.

Adenosine Triphosphate↗
PubMed1996

Potassium transport: from clearance to channels and pumps.

Potassium (K) homeostasis depends on the separate and interrelated regulation of K distribution between the intra- and extra-cellular fluid compartments and adequate renal excretion. This brief review focuses on the regulation of internal K distribution and the renal mechanisms of K handling. Based on clearance, micropuncture, and microperfusion studies, a large body of evidence supports the view that normally, renal secretion of K determines excretion and that the principal tubule cells in the initial and cortical collecting tubule secrete K, whereas K reabsorption may occur in intercalated cells. Studies of the electrochemical driving forces, of intracellular ion activities, the characterization of several ATPases, and patch clamp investigations have provided insight into the role of pumps and channels in those tubule cells that regulate K secretion and reabsorption.

Animals↗
PubMed1996

Effects of angiotensin II on electrolyte transport in the early and late distal tubule in rat kidney.

We have demonstrated in previous studies that luminal administration of low doses of angiotensin II (ANG II) stimulate and high doses of ANG II inhibit fluid and HCO3- transport in proximal tubules of rat kidney. However, the role of ANG II on Na+ and HCO3- transport in the distal nephron has not yet been fully elucidated. The superficial early and late distal tubules (DT) of the nephron segments correspond to the distal convoluted tubule and initial collecting tubule. Accordingly, we investigated the effects of ANG II on Na+, HCO3-, and K+ transport in the early and late DT by separate perfusion of these tubule segments in vivo. [3H]inulin, Na+, K+, and total CO2 concentrations were measured in the perfusate and collected fluid, and transport of sodium (JNa), bicarbonate (JHCO3), potassium (JK), and fluid (JV) were analyzed as an index of the hormone effect. Intravenous infusion of the ANG II receptor antagonist [Sar1,Ile8]ANG II (1 microgram.kg-1.min-1) decreased JV, JNa, and JHCO3 in the early DT and decreased Jv and JNa in the late DT. Addition of ANG II (10(-11) M) to the tubular perfusate significantly increased the Jv, JNa, and JHCO3 in the early DT. Similar studies in late DT demonstrated an increase in Jv and JNa, decrease in JK, but no effect on JHCO3. The effects of ANG II on fluid and ion transport were abolished by the luminal application of amiloride (10(-3) M) and of the angiotensin-receptor blocker [Sar1,Ile8]ANG II (10(-6) M). These results suggest that ANG II stimulates Na+/H+ exchange in the early DT (distal convoluted tubule) and amiloride-sensitive Na+ transport (Na+ channels) in the late DT (initial collecting tubule) of cortical nephrons.

Angiotensin II↗
PubMed1996

Aldosterone-dependent regulation of Na-K-ATPase subunit mRNA in the rat CCD: competitive PCR analysis.

In the cortical collecting duct (CCD), aldosterone increases the number of functionally active Na-K-adenosin-etriphosphatase (Na-K-ATPase) molecules by a mechanism involving an isoform-specific increase in the abundance of the Na-K-ATPase alpha 1- and beta 1-subunit protein. However, the molecular basis for the response, particularly in the mammalian CCD in vivo, has remained unclear. To resolve this issue, reverse transcription (RT) and a competitive polymerase chain reaction (PCR) were employed to study mineralocorticoid-dependent regulation of alpha 1- and beta 1-subunit mRNA in the rat CCD. Na-K-ATPase subunit-specific oligonucleotides primers were used in the PCR to amplify reverse-transcribed subunit mRNA (RT-mRNA) from single microdissected CCD. Control templates were constructed (84-bp deletion mutation of the rat Na-K-ATPase alpha 1-subunit cDNA and 70-bp deletion of the beta 1-subunit cDNA), serially diluted, and coamplified with the wild-type Na-K-ATPase subunit RT-mRNA from single CCD. PCR products of predicted size were observed by ethidium bromide staining. Southern blots with an internal subunit-specific oligonucleotide confirmed Na-K-ATPase alpha 1- and beta 1-subunit identity. The ratio of the amplified wild-type to mutant PCR products was found to be linear over the range of input control cDNA tested so that the amount of subunit mRNA could be determined. A chronic reduction in corticosteroid levels by bilateral adrenalectomy (7 days) reduced the apparent level of alpha 1-subunit transcript by 54.0 +/- 6.3% but not the beta 1-subunit. Administering aldosterone to physiological levels is sufficient to restore CCD alpha 1-subunit mRNA abundance toward control levels within 6 h. We conclude the following: 1) regulation of Na-K-ATPase of CCD in vivo can be attributed, at least in part, to mineralocorticoid-dependent control of Na-K-ATPase alpha 1-subunit mRNA abundance; and 2) competitive PCR may provide a sensitive and quantitative tool for determining hormone-dependent regulation of mRNA abundance in nephron segments.

Adrenalectomy↗
PubMed1996

Molecular site for nucleotide binding on an ATP-sensitive renal K+ channel (ROMK2).

ATP-sensitive, inwardly rectifying K+ channels are present in apical membranes of the distal nephron and play a major role in K+ recycling and secretion. The cloned renal K+ channel, ROMK1, is a candidate for the renal epithelial K+ channel, since it shares many functional characteristics with the native channel. Additionally, ROMK1 contains a putative carboxy-terminal ATP-binding site. Although ROMK1 channel activity could be reactivated by cytosolic Mg-ATP after rundown, the role of nucleotides in channel gating was less certain. We now show that an alternatively spliced transcript of the ROMK channel gene, ROMK2, which encodes a K+ channel with a truncated amino terminus, expresses an ATP-regulated and ATP-sensitive K+ channel (IKATP). Differences in the amino terminus of ROMK isoforms alters the sensitivity of the channel-gating mechanism to ATP. To test whether ATP sensitivity of renal IKATP is mediated by direct interaction of nucleotide, point mutation of specific residues within the ROMK2 phosphate loop (P-loop) were investigated. These either enhanced or attenuated the sensitivity to both activation and inhibition by Mg-ATP, thus demonstrating a direct interaction of nucleotide with the channel-forming polypeptide.

Adenosine Triphosphate↗
PubMed1996

Mechanisms of stimulation of proximal tubule chloride transport by formate and oxalate.

We have previously demonstrated that formate and oxalate stimulate volume absorption in the rat proximal tubule, consistent with Cl-/formate and Cl-/oxalate exchange process across the apical membrane. To sustain Cl- absorption by these processes requires mechanisms for recycling formate and oxalate from lumen to cell. The aims of the present study were to characterize these mechanisms of formate and oxalate recycling. Proximal tubules and peritubular capillaries were simultaneously microperfused in the rat kidney in situ. Serum formate concentration was determined to be 56.5 +/- 7.7 microM. Addition of 5, 50, and 500 microM formate to both luminal and capillary perfusates significantly increased net Cl- absorption (Jcl) by 26, 26, and 46%, respectively. Jcl was stimulated 38% by 1 microM oxalate added to the perfusates. Removal of sulfate completely prevented the stimulation of Jcl by 1 microM oxalate but had no effect on the stimulation of Jcl by formate. Luminal addition of the Na+/H+ exchange inhibitor ethylisopropylamiloride completely blocked the stimulation of Jcl by 50 microM formate but had no effect on stimulation by oxalate. We conclude that physiological concentrations of formate and oxalate markedly stimulate Cl- and fluid absorption in the rat proximal convoluted tubule. Whereas formate recycling most likely involves Na+/H+ exchange in parallel with H(+)-coupled formate entry, oxalate recycling involves sodium-sulfate cotransport in parallel with sulfate/oxalate exchange.

Amiloride↗
PubMed1996

Model development and analysis of tenidap-induced proteinuria in the rat.

Tenidap is a novel antirheumatic agent that causes a mild, reversible proteinuria in human clinical trials. In order to achieve a mechanistic understanding and safety perspective of the proteinuric effects of tenidap observed in clinical trials, female Sprague-Dawley rats were treated with up to 100 mg/kg/day of tenidap in the diet for 4 to 6 weeks followed by a 1- to 6-week reversal period. Pharmacokinetics and measurements of renal function and histology were assessed during the study. Sustained high plasma concentrations of tenidap [area under the plasma concentration curve (0-24 hr) of 941-1021 micrograms. hr/ml and peak plasma concentration of 61-67 micrograms/ml] increased urinary protein, albumin and phosphate excretion (2- to 8-fold) in rats. These renal effects were reversible within 9 days after removal of the drug. These effects preceded later occurring changes in renal morphology (papillary degeneration and necrosis). There was no evidence of glomerular damage, proximal tubule degeneration or necrosis or tubulointerstitial nephritis at the light microscopic level. Other indices of overall renal function (glomerular filtration rate, electrolyte and glucose excretion) were unaffected. Examination in situ of microperfused proximal tubules from treated rats revealed a 68% decrease in the rate of proximal tubule albumin absorption compared to controls (19 +/- 4 vs. 59 +/- 7 pg/min/mm, respectively). Fluid absorption rate and bicarbonate handling by the proximal tubule, along with blood bicarbonate concentrations, pH, PCO2 and PO2, were unaffected by treatment. It was concluded that tenidap caused a rapid, stable and reversible phosphaturia, microalbuminuria and proteinuria in the rat. The proteinuric effects were due to impaired proximal tubule albumin reabsorption that were not associated with other signs of impaired renal function or histological evidence of tubulointerstitial nephritis or proximal tubule/glomerular damage.

Albumins↗
PubMed1995

Effects of chronic hyperfiltration on proximal tubule bicarbonate transport and cell electrolytes.

The compensatory response to unilateral nephrectomy (UNX) was investigated by a combination of renal clearance, microperfusion, electron microprobe, and morphological techniques. Filtration rate was significantly elevated 21 days following UNX and associated with a marked stimulation of bicarbonate and fluid absorption in the proximal tubule. Analysis of kinetic data of bicarbonate transport demonstrated strong flow-dependent activation of bicarbonate absorption in both control and experimental condition. The bicarbonate level at which half-saturation (apparent Kd) of transport occurred decreased uniformly at higher flow rates, but maximal transport rates (apparent Vmax) in the proximal tubule doubled in the remnant kidney. The flow dependence of bicarbonate transport in control and experimental conditions can be explained by an apparent unstirred layer effect modifying radial bicarbonate gradients in the tubule. Both Na/H-exchange and electrogenic H secretion contribute to bicarbonate absorption, but only Na/H-exchange increased significantly in proximal tubules of UNX rats. Cell ion concentrations after UNX were unchanged in cortical tubules, consistent with proportionately enhanced apical and basolateral ion transport. Proximal tubule cell rubidium concentration measured after a 30-second rubidium infusion as an index of basolateral Na,K-ATPase activity was unchanged in UNX rats. Inasmuch as cell volume increased significantly (25%), these data are consistent with a proportionate and similar stimulation of rubidium uptake and Na,K-ATPase activity.

Animals↗
PubMed1995

Visualizing life on biomembranes by atomic force microscopy.

Since its invention in 1986, the atomic force microscope (AFM) has become one of the most widely used near-field microscopes. Surfaces of hard samples are imaged routinely with atomic resolution. Soft biological samples, however, are still challenging. In this brief review, the AFM technique is introduced to the experimental biologist. We discuss recent data on imaging molecular structures of biomembranes, and give detailed information on the application of the AFM with two representative examples. One is imaging plasma membrane turnover of transformed renal epithelial cells during migration in vivo, and the other is visualizing macromolecular pore complexes of the nuclear envelope of aldosterone-sensitive kidney cells.

Animals↗
PubMed1995

Stimulation of chloride transport by cAMP in rat proximal tubules.

We have previously demonstrated that formate and oxalate stimulate transcellular Cl- absorption (JCl) in the rat proximal tubule by a mechanism involving DIDS-sensitive anion exchange across the luminal membrane and diphenylamine-2-carboxylate (DPC)-sensitive Cl- channels in the basolateral membrane. Recent evidence indicates cAMP activation of Cl- channels in apical and basolateral membranes of proximal tubule cells. We therefore tested the effect of cAMP on Cl- and fluid transport in rat proximal tubule studied by luminal and capillary microperfusion in situ. The luminal perfusate contained 5 mM HCO3- and 145 mM Cl-, and the capillary perfusate contained 25 mM HCO3- and 110 mM Cl-, simulating conditions in the late proximal tubule. Addition of 0.5 mM dibutyryl cAMP markedly stimulated fluid absorption (Jv) and JCl. Similar effects resulted from addition of forskolin (10 microM) to stimulate cAMP production. The increments in Jv and JCl due to dibutyryl cAMP were abolished when the Cl- channel blocker DPC (200 microM) was added to the capillary perfusate but not when it was added to the lumen. The increments in Jv and JCl due to dibutyryl cAMP were unaffected by luminal DIDS (100 microM), which abolishes the increments in Jv and JCl induced by addition of oxalate. In contrast, the increments in Jv and JCl due to dibutyryl cAMP were abolished by luminal 5-nitro-2-(3-phenylpropylamino)benzoate (NPPB; 10 microM), another Cl- channel blocker. Luminal NPPB had no effect on baseline Jv and JCl nor on the increments in Jv and JCl induced by addition of oxalate.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗
PubMed1995

Role of Ca2+/CaMK II in Ca(2+)-induced K+ channel inhibition in rat CCD principal cell.

The apical low-conductance K+ channel of rat cortical collecting duct (CCD) is inhibited by increased intracellular Ca2+ concentrations. This effect has been shown to be mediated at least in part by activation of protein kinase C (PKC). In the present study, we used the patch-clamp technique to examine the role of Ca2+/calmodulin-dependent protein kinase II (CaMK II) in mediating the Ca(2+)-induced inhibitory effect. In cell-attached patches of principal cells of rat tubules, clamping of intracellular Ca2+ concentration at 400 nM by using 1 microM ionomycin reduced channel activity to 26.5% of the control value. A further reduction in channel activity, to 8.8% of the control value, was observed following the addition of phorbol 12-myristate 13-acetate (PMA), an agent known to activate PKC. Pretreatment of cells with KN-62 (CaMK II inhibitor) or GF-109203X (PKC inhibitor) attenuated the inhibitory effect of Ca2+ on K+ channel activity (83.2 and 50.7% of the control value, respectively). Even in the presence of KN-62, addition of 10 microM PMA significantly decreased channel activity to 57.2% of the control value. The Ca(2+)-induced inhibition was completely abolished by simultaneous incubation with both KN-62 and GF-109203X. In inside-out patches, addition of 20 micrograms/ml CaMK II in the presence of a PKC inhibitor reduced channel activity to 66.2% of control values. It is concluded that CaMK II is involved in mediating the Ca(2+)-induced inhibition of the activity of the apical K+ channel of rat CCD.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1995

Bicarbonate transport along the loop of Henle effects of adrenal steroids.

The role of adrenal steroids in the regulation of bicarbonate absorption in the loop of Henle was studied by in vivo microperfusion. Bicarbonate transport (JHCO3) was measured by microcalorimetry and fluid reabsorption by [14C]inulin, 7-10 days after surgery, in 1) sham-operated control rats, 2) adrenalectomized (Adx) rats, 3) Adx rats receiving dexamethasone (1.2 micrograms.100 g body wt-1.24 h-1) and a low dose of aldosterone (0.5 micrograms.100 g body wt-1.24 h-1), 4) Adx rats receiving dexamethasone, 5) Adx rats receiving a low dose of aldosterone, and 6) Adx rats receiving a high dose of aldosterone (1.0 micrograms.100 g body wt-1.24 h-1). JHCO3 along the loop of Henle was decreased by 40% in Adx rats. JHCO3 was increased by dexamethasone alone and by dexamethasone plus a low dose of aldosterone to rates observed in fully supplemented Adx rats. Aldosterone given alone at a low physiological dose had no effect, but, when administered at a high dose, returned JHCO3 to normal.

Absorption↗
PubMed1995

Regulation of ATP-sensitive K+ channel by membrane-bound protein phosphatases in rat principal tubule cell.

The role of membrane-bound protein serine/threonine phosphatases (PP) in modulating the renal ATP-sensitive K+ (KATP) channel was examined using the patch-clamp technique in principal cells of rat cortical collecting duct. In the absence of ATP, channel activity rapidly (11.2 s) declines (channel "rundown") upon excision of the membrane patches into control bath solutions (1 mM Mg2+, Ca2+ free). Both orthovanadate (5 mM), a broad-spectrum inhibitor of phosphatases except for Ca(2+)-dependent PP (PP-2B), and okadaic acid (OA, 1 microM), a potent inhibitor of PP types 1 and 2A (PP-1 and PP-2A), significantly slowed channel rundown. Removal of Mg2+ from the bath also slowed the rundown process. Incubation of cells with OA in the absence of Mg2+ or with orthovanadate in ATP-free solution maintained channel activity at levels of approximately 70% of control values for 3 min after membrane excision. In contrast, Ca2+ (0.1 mM) and calmodulin (1 microM) in the presence of 1 mM Mg2+, a condition in which PP-2B is stimulated, had no significant effect on the channel activity that persisted in the presence of OA and orthovanadate. Application of exogenous PP-2A (1 U/ml) to the cytosolic side of membrane in inside-out patches significantly inhibited channel activity to 35.0% of control, but the inhibitory-effects of PP-1 (1 U/ml) and PP-2B (20 micrograms/ml) were minor. These results suggest that rundown of the renal KATP channel after membrane excision results mainly from dephosphorylation of the channel or an associated protein by membrane-bound phosphatases.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗