Modulation of K<sup>+</sup> conductance by intracellular pH in pancreatic β‐cells

Rosário, Luı́s M.; Rojas, Eduardo

doi:10.1016/0014-5793(86)80539-7

Cited by 26 publications

(10 citation statements)

References 36 publications

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“…Studies in frog skeletal muscle [5], in squid giant axon [33], in rat and mouse pancreatic/3-cells [7,28], in rat lens [3], in retinal pigment epithelium [l 1], and in Amphiuma diluting segment I11] indicate that K + channels are blocked by internal H + ions independent of whether the external bath is made more acidic or basic. This suggests the existence of titratable groups at the inner (cytoplasmic) face of the K + channel proteins.…”

Section: Discussionmentioning

confidence: 99%

Fusion of cultured dog kidney (MDCK) cells: II. Relationship between cell pH and K+ conductance in response to aldosterone

et al. 1989

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We have chosen the MDCK cell line to investigate aldosterone action on H+ transport and its role in regulating cell membrane K+ conductance (GKm). Cells grown in a monolayer respond to aldosterone indicated by the dose-dependent formation of domes and by the alkalinization of the dome fluid. The pH sensitivity of the plasma membrane K+ channels was tested in "giant cells" fused from individual MDCK cells. Cytoplasmic pH (pHi) and GKm were measured simultaneously while the cell interior was acidified gradually by an extracellular acid load. We found a steep sigmoidal relationship between pHi and GKm (Hill coefficient 4.4 +/- 0.4), indicating multiple H+ binding sites at a single K+ channel. Application of aldosterone increased pHi within 120 min from 7.22 +/- 0.04 to 7.45 +/- 0.02 and from 7.15 +/- 0.03 to 7.28 +/- 0.02 in the absence and presence of the CO2/HCO-3 buffer system, respectively. We conclude that the hormone-induced cytoplasmic alkalinization in the presence of CO2/HCO-3 is limited by the increased activity of a pHi-regulating HCO-3 extrusion system. Since GKm is stimulated half-maximally at the pHi of 7.18 +/- 0.04, internal H+ ions could serve as an effective intracellular signal for the regulation of transepithelial K+ flux.

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Section: Discussionmentioning

confidence: 99%

Fusion of cultured dog kidney (MDCK) cells: II. Relationship between cell pH and K+ conductance in response to aldosterone

et al. 1989

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“…The passive membrane conductance of early distal tubule cells is determined by Cl-and K+ channels (7 Inhibition of cell-membrane K+ conductance by acidification of the cytoplasmic membrane surface has been shown in perfused squid giant axon (9) and more recently in pancreatic B cells (10,11). The fused cell preparation allows simultaneous measurements of intracellular pH and cell membrane GK in the renal epithelium.…”

Section: Resultsmentioning

confidence: 99%

Cytoplasmic pH determines K+ conductance in fused renal epithelial cells.

Oberleithner

Kersting

Hunter

1988

Proc. Natl. Acad. Sci. U.S.A.

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The mineralocorticoid hormone aldosterone maintains acid-base balance and K + homeostasis by regulating H + and K + secretory mechanisms in kidney epithelial cells. We have shown recently in the amphibian distal nephron that aldosterone activates a Na + /H + exchange system in the luminal cell membrane, thus leading to transepithelial H+ secretion and cytoplasmic alkalinization. Since H+ secretory fluxes were paralleled by K + secretion, it was postulated that the hormone-induced increase of intracellular pH activates the luminally located K+ channels. In "giant" cells fused from individual cells of the distal nephron, we measured simultaneously cytoplasmic pH and cell membrane K+ conductance during acidification of the cell cytoplasm. The experiments show that cell membrane K+ conductance is half-maximal at an intracellular pH of 7.42 and that a positive cooperative interaction exists between K+-channel proteins and H+ (Hill coefficient = 6.5). Moreover, the cellular K+ conductance is most sensitive to cytoplasmic pH in the range modified by aldosterone. This supports the hypothesis that intracellular H + activity, regulated by the Na +/H+ exchanger, serves as the signal to couple aldosterone-induced K + secretory flux to H + secretion in renal tubules.In the vertebrate kidney, aldosterone stimulates Na+ retention and H + and K + secretion. In the collecting duct system of the mammalian kidney, aldosterone stimulates Na + entry across the luminal cell membrane (1), thereby depolarizing the cell membrane potential (2). This depolarization facilitates cell-to-lumen K+ secretion (3) via hormone-activated (4) K +-selective channels and H + extrusion via a rheogenic H + pump (5). From experiments in the early distal nephron of the amphibian kidney, we have evidence that transepithelial fluxes of Na+, K+, and H+ ions are also functionally linked, but that the mechanisms involved are different from those in the mammalian collecting-duct system (6).We propose a model in which hormone-induced stimulation of the Na +/H + exchanger is the primary event leading to cytoplasmic alkalinization and subsequent activation of the pH-sensitive K + channels. Ifthe mechanism whereby the hormone-induced interaction between a counter-transport mechanism (Na +/H + exchanger) and an ionic channel (K + channel) is to be physiologically relevant, the K + channels must be sensitive to intracellular pH (pH;) within the range encompassed during exposure to the hormone (7.45-7.73). METHODSTo test our hypothesis, we simultaneously measured the intracellular pH and K + -conductance of fused distal tubules from frog kidney during gradual acidification of the cytoplasm.The fusion procedure has been described elsewhere (6). Briefly, kidneys of Rana pipiens were first isolated and perfused with amphibian Ringer's solution composed of 97 mM NaCl, 3 mM KCI, 5 mM Hepes, 1 mM CaC12, 1 mM MgCl2, and 5 mM glucose. After the blood was rinsed off, 3 ml of the same solution containing 0.1% collagenase [Sigma or Seromed (Berlin); 180-300 units/mg] wa...

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“…These channels are seen to open at high depolarizing voltages in the cell-attached patch (see Cook, Ikeuchi & Fujimoto, 1984;Findlay, Dunne & Petersen., 1985;Tabcharani & Misler, 1989). Gating of these channels by pH has previously been considered as the source of cell depolarization induced by weak acids and cell hyperpolarization induced by weak bases (Rosario & Rojas, 1986b). K+(Ca 2+) channels in inside-out excised patches from neonatal mouse islet cells have been reported to be activated by elevated phi and suppressed by reduced pHi over the range of pH 8.0 to 6.0 .…”

Section: Lack Of Effect Of Alteration Of Phi On Other K + Channels 1nmentioning

confidence: 98%

“…This idea stems from evidence that (i) cellular metabolism can generate protons; (ii) intracellular pH can alter cell potassium permeability; and (iii) bath-applied membrane-permeant weak acids and bases can modulate metabolite-induced changes in PK+, electrical activity and insulin secretion, perhaps by acidifying or alkalinizing the cell (Eddlestone & Beigelman+ 1983;Smith & Pace, 1983;Pace, 1984b;Rosario & Rojas, 1986b). Measurements of changes in intracellular pH during glucose metabolism has been attempted in several insulin secreting cells; results vary, however, from a small increase, to small decreases, to no change.…”

Section: Introductionmentioning

confidence: 99%

Modulation of gating of a metabolically regulated, ATP-dependent K+ channel by intracellular pH in B cells of the pancreatic islet

1989

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Membrane-permeant weak acids and bases, when applied to the bath, modulate the resting membrane potential and the glucose-induced electrical activity of pancreatic B cells, as well as their insulin secretion. These substances alter the activity of a metabolite-regulated, ATP-sensitive K+ channel which underlies the B-cell resting potential. We now present several lines of evidence indicating that the channel may be directly gated by pHi. (1) The time course of K+(ATP) channel activity during exposure to and washout of NH4Cl under a variety of experimental conditions, including alteration of the electrochemical gradient for NH4Cl entry and inhibition of the Na+o/H+i exchanger, resembles the time course of pHi measured in other cell types that have been similarly treated. (2) Increasing pHo over the range 6.25-7.9 increases K+(ATP) channel activity in cell-attached patches where the cell surface exposed to the bath has been permeabilized to H+ by the application of the K+/H+ exchanger nigericin. (3) Increasing pHi over a similar range produces similar effects on K+(ATP) channels in inside-out excised patches exposed to small concentrations of ATPi. The physiological role of delta pHi in the metabolic gating of this channel remains to be explored.

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Modulation of K⁺ conductance by intracellular pH in pancreatic β‐cells

Cited by 26 publications

References 36 publications

Fusion of cultured dog kidney (MDCK) cells: II. Relationship between cell pH and K+ conductance in response to aldosterone

Fusion of cultured dog kidney (MDCK) cells: II. Relationship between cell pH and K+ conductance in response to aldosterone

Cytoplasmic pH determines K+ conductance in fused renal epithelial cells.

Modulation of gating of a metabolically regulated, ATP-dependent K+ channel by intracellular pH in B cells of the pancreatic islet

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Modulation of K+ conductance by intracellular pH in pancreatic β‐cells

Cited by 26 publications

References 36 publications

Fusion of cultured dog kidney (MDCK) cells: II. Relationship between cell pH and K+ conductance in response to aldosterone

Fusion of cultured dog kidney (MDCK) cells: II. Relationship between cell pH and K+ conductance in response to aldosterone

Cytoplasmic pH determines K+ conductance in fused renal epithelial cells.

Modulation of gating of a metabolically regulated, ATP-dependent K+ channel by intracellular pH in B cells of the pancreatic islet

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Modulation of K⁺ conductance by intracellular pH in pancreatic β‐cells