Involvement of Endogenous Nitric Oxide in the Regulation of K+ Channel Activity in Cultured Human Proximal Tubule Cells

An ATP-regulated inwardly rectifying K+ channel, whose activity is enhanced by PKA, is present in the plasma membrane of cultured human proximal tubule cells. In this study, we investigated the effects of PKG on this K+ channel, using the patch-clamp technique. In cell-attached patches, bath application of a membrane-permeant cGMP analog, 8-bromoguanosine 3′,5′-monophosphate (8-BrcGMP; 100 μM), stimulated channel activity, whereas application of a PKG-specific inhibitor, KT-5823 (1 μM), reduced the activity. Channel activation induced by 8-BrcGMP was observed even in the presence of a PKA-specific inhibitor, KT-5720 (500 nM), which was abolished by KT-5823. Direct effects of cGMP and PKG were examined with inside-out patches in the presence of 1 mM MgATP. Although cytoplasmic cGMP (100 μM) alone had little effect on channel activity, subsequent addition of PKG (500 U/ml) enhanced it. Furthermore, bath application of atrial natriuretic peptide (ANP; 20 nM) in cell-attached patches stimulated channel activity, which was blocked by KT-5823. In conclusion, cGMP/PKG-dependent processes participate in activating the ATP-regulated K+ channel and producing the stimulatory effect of ANP on channel activity.

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Proinflammatory Cytokines and Potassium Channels in the Kidney

Mediators of Inflammation ◽

10.1155/2015/362768 ◽

2015 ◽

Vol 2015 ◽

pp. 1-8 ◽

Cited By ~ 4

Author(s):

Kazuyoshi Nakamura ◽

Hikaru Hayashi ◽

Manabu Kubokawa

Keyword(s):

Proximal Tubule ◽

Proinflammatory Cytokines ◽

Transforming Growth Factor ◽

Interleukin 1 ◽

Transepithelial Transport ◽

Channel Activity ◽

Proximal Tubule Cells ◽

Cell Functions ◽

Tubule Cells ◽

Human Proximal Tubule

Proinflammatory cytokines affect several cell functions via receptor-mediated processes. In the kidney, functions of transporters and ion channels along the nephron are also affected by some cytokines. Among these, alteration of activity of potassium ion (K+) channels induces changes in transepithelial transport of solutes and water in the kidney, since K+channels in tubule cells are indispensable for formation of membrane potential which serves as a driving force for the transepithelial transport. Altered K+channel activity may be involved in renal cell dysfunction during inflammation. Although little information was available regarding the effects of proinflammatory cytokines on renal K+channels, reports have emerged during the last decade. In human proximal tubule cells, interferon-γshowed a time-dependent biphasic effect on a 40 pS K+channel, that is, delayed suppression and acute stimulation, and interleukin-1βacutely suppressed the channel activity. Transforming growth factor-β1 activated KCa3.1 K+channel in immortalized human proximal tubule cells, which would be involved in the pathogenesis of renal fibrosis. This review discusses the effects of proinflammatory cytokines on renal K+channels and the causal relationship between the cytokine-induced changes in K+channel activity and renal dysfunction.

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An ATP-Regulated and pH-Sensitive Inwardly Rectifying K+ Channel in Cultured Human Proximal Tubule Cells.

The Japanese Journal of Physiology ◽

10.2170/jjphysiol.51.523 ◽

2001 ◽

Vol 51 (4) ◽

pp. 523-530 ◽

Cited By ~ 9

Author(s):

Kazuyoshi Nakamura ◽

Junko Hirano ◽

Manabu Kubokawa

Keyword(s):

Proximal Tubule ◽

Ph Sensitive ◽

K Channel ◽

Proximal Tubule Cells ◽

Tubule Cells ◽

Inwardly Rectifying ◽

Human Proximal Tubule

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Properties of an Inwardly Rectifying ATP-sensitive K+ Channel in the Basolateral Membrane of Renal Proximal Tubule

The Journal of General Physiology ◽

10.1085/jgp.111.1.139 ◽

1998 ◽

Vol 111 (1) ◽

pp. 139-160 ◽

Cited By ~ 35

Author(s):

Ulrich R. Mauerer ◽

Emile L. Boulpaep ◽

Alan S. Segal

Keyword(s):

Proximal Tubule ◽

Basolateral Membrane ◽

Potassium Conductance ◽

Physiological Role ◽

K Channel ◽

Nucleoside Triphosphate ◽

Channel Activity ◽

Open Probability ◽

Proximal Tubule Cells ◽

Tubule Cells

The potassium conductance of the basolateral membrane (BLM) of proximal tubule cells is a critical regulator of transport since it is the major determinant of the negative cell membrane potential and is necessary for pump-leak coupling to the Na+,K+-ATPase pump. Despite this pivotal physiological role, the properties of this conductance have been incompletely characterized, in part due to difficulty gaining access to the BLM. We have investigated the properties of this BLM K+ conductance in dissociated, polarized Ambystoma proximal tubule cells. Nearly all seals made on Ambystoma cells contained inward rectifier K+ channels (γslope, in = 24.5 ± 0.6 pS, γchord, out = 3.7 ± 0.4 pS). The rectification is mediated in part by internal Mg2+. The open probability of the channel increases modestly with hyperpolarization. The inward conducting properties are described by a saturating binding–unbinding model. The channel conducts Tl+ and K+, but there is no significant conductance for Na+, Rb+, Cs+, Li+, NH4+, or Cl−. The channel is inhibited by barium and the sulfonylurea agent glibenclamide, but not by tetraethylammonium. Channel rundown typically occurs in the absence of ATP, but cytosolic addition of 0.2 mM ATP (or any hydrolyzable nucleoside triphosphate) sustains channel activity indefinitely. Phosphorylation processes alone fail to sustain channel activity. Higher doses of ATP (or other nucleoside triphosphates) reversibly inhibit the channel. The K+ channel opener diazoxide opens the channel in the presence of 0.2 mM ATP, but does not alleviate the inhibition of millimolar doses of ATP. We conclude that this K+ channel is the major ATP-sensitive basolateral K+ conductance in the proximal tubule.

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