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  • K+ channel  (6)
  • Animals
  • Coleus (cell cultures)
  • METEOROLOGY AND CLIMATOLOGY
  • Springer  (8)
  • 1
    Electronic Resource
    Electronic Resource
    ATP-sensitive K+ channels in an insulin-secreting cell line are inhibited byd-glyceraldehyde and activated by membrane permeabilization (1986)
    Springer
    The journal of membrane biology 93 (1986), S. 271-279 
    Details
    ISSN: 1432-1424
    Keywords: K+ channel ; ATP ; glyceraldehyde ; RINm5F cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The control of K+ channels in the insulin-secreting cell line RINm5F has been investigated by patch-clamp singlechannel current recording experiments. The unitary current events recorded from cell-attached patches are due to large and small inwardly rectifying ATP-sensitive K+ channels with conductance properties similar to the two channels previously identified in primary cultured rat islet cells (Findlay, I., Dunne, M.J., & Petersen, O. H.J. Membrane Biol. 88:165–172, 1985). Cell permeabilization through brief exposure to 10 μm digitonin or 0.05% saponin (outside the isolated membrane patch area) results in a dramatic increase in current through the cell-attached patch due to opening of many large and small K+-selective channels. These channels are inhibited in a dose-dependent manner by ATP applied to the bath (near-complete inhibition by 5mm ATP). During prolonged ATP exposure (1–5 min) the initial inhibition is followed by partial recovery of channel activity, although further activation does occur when ATP is subsequently removed. From the maximal number of coincident channel openings in the permeabilized cells (in the absence of ATP), it is estimated that there are on average 12 large ATP-sensitive K+ channels per membrane patch, but in the intact cells less than 5% of the membrane patches exhibited three or more coincident K+ channel openings, indicating the degree to which the channels are inhibited in the resting condition by endogenous ATP. Stimulation of RINm5F cells to secrete insulin was carried out by challenging intact cells with 10mm d-glyceraldehyde.d-glyceraldehyde induced depolarization of the membrane from about −70 to −20 mV and evoked a marked reduction in the open-state probability of both the large and small ATP-sensitive channels.d-glyceraldehyde also induced action potentials in a number of cases. All effects of stimulation were largely transient, lasting about 100 sec. The two ATP-sensitive K+ channels are probably responsible for the resting potential and play a crucial role in coupling metabolism to membrane depolarization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871181
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  • 2
    Electronic Resource
    Electronic Resource
    Purification of rosmarinic acid synthase from cell cultures of Coleus blumei Benth (1993)
    Springer
    Planta 191 (1993), S. 18-22 
    Details
    ISSN: 1432-2048
    Keywords: Coleus (cell cultures) ; Hydroxycinnamic acid ester ; Rosmarinic acid ; Rosmarinic acid synthase (purification)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Rosmarinic acid synthase from cell cultures of Coleus blumei Benth. was purified to apparent homogeneity by fractionated ammonium sulfate precipitation (60–80% saturation), hydrophobic interaction chromatography, affinity chromatography and gel filtration. This purification procedure resulted in a 225-fold-enriched specific enzyme activity with a yield of 9%. The protein preparation was apparently pure according to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and two-dimensional gel electrophoresis. The apparent molecular mass determined by gel filtration and SDS-PAGE was 77 kDa, indicating that rosmarinic acid synthase is a monomeric enzyme.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00240891
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  • 3
    Electronic Resource
    Electronic Resource
    Proposed biosynthetic pathway for rosmarinic acid in cell cultures of Coleus blumei Benth (1993)
    Springer
    Planta 189 (1993), S. 10-14 
    Details
    ISSN: 1432-2048
    Keywords: Coleus (cell cultures) ; Hydroxycinnamic acid ester ; Phenylpropanoid metabolism ; Rosmarinic acid (biosynthetic pathway)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A biosynthetic pathway for rosmarinic acid is proposed. This pathway is deduced from studies of the enzymes detectable in preparations from suspension cells of Coleus blumei. Phenylalanine is transformed to 4-coumaroyl-CoA by the enzymes of the general phenylpropanoid pathway: phenylalanine ammonia-lyase (EC 4.3.1.5), cinnamic acid 4-hydroxylase (EC 1.14.13.11) and hydroxycinnamic acid:CoA ligase (EC 6.2.1.12). Tyrosine is metabolized to 4-hydroxyphenyllactate by tyrosine aminotransferase (EC 2.6.1.5) and hydroxyphenylpyruvate reductase. The ester can be formed from 4-coumaroyl-CoA and 4-hydroxyphenyllactate by the catalytic activity of rosmarinic acid synthase with concomitant release of CoA. Microsomal hydroxylase activities introduce the hydroxyl groups at positions 3 and 3′ of the aromatic rings of the ester 4-coumaroyl-4′-hydroxyphenyllactate giving rise to rosmarinic acid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201337
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of pyridine nucleotides on the gating of ATP-sensitive potassium channels in insulin-secreting cells (1988)
    Springer
    The journal of membrane biology 102 (1988), S. 205-216 
    Details
    ISSN: 1432-1424
    Keywords: K+ channel ; ATP ; NAD(P) ; NAD(P)H ; RINm5F cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The single-channel current recording technique has been used to study the influences that the pyridine nucleotides NAD, NADH, NADP and NADPH have on the gating of ATP-sensitive K+ channels in an insulin-secreting cell line (RINm5F). The effects of the nucleotides were studied at the intracellular surface using either excised inside-out membrane patches or permeabilized cells. All four pyridine nucleotides were found to evoke similar effects. At low concentrations, 100 μm and less, each promoted channel opening whereas high concentrations, 500 μm and above, evoked channel closure. The degree of K+ channel activation by pyridine nucleotides (low conc.) was found to be similar to that evoked by the same concentrations of ADP or GTP, whereas the degree of K+ channel inhibition (high conc.) was less marked than that evoked by the same concentrations of ATP, and never resulted in refreshment of K+ channels following removal. The effects of NAD, NADH, NADP and NADPH seemed to interact with those of ATP and ADP. In the presence of 1mm ADP and 4mm ATP, 10 to 100 μm concentrations of the pyridine nucleotides could not evoke channel opening, whereas concentrations of 500 μm and above were found to evoke channel closure. In the presence of 2mm ATP and 0.5mm ADP, however, 10 to 100 μm concentrations of the pyridine nucleotides were able to activate K+ channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01925714
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  • 5
    Electronic Resource
    Electronic Resource
    High-conductance K+ channel in pancreatic islet cells can be activated and inactivated by internal calcium (1985)
    Springer
    The journal of membrane biology 83 (1985), S. 169-175 
    Details
    ISSN: 1432-1424
    Keywords: pancreatic islet cells ; K+ channel ; patchclamp ; single-channel recording ; Ca2+ activation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The Ca2+-activated K+ channel in rat pancreatic islet cells has been studied using patch-clamp single-channel current recording in excised inside-out and outside-out membrane patches. In membrane patches exposed to quasi-physiological cation gradients (Na+ outside, K+ inside) large outward current steps were observed when the membrane was depolarized. The single-channel current voltage (I/V) relationship showed outward rectification and the null potential was more negative than −40 mV. In symmetrical K+-rich solutions the single-channelI/V relationship was linear, the null potential was 0 mV and the singlechannel conductance was about 250 pS. Membrane depolarization evoked channel opening also when the inside of the membrane was exposed to a Ca2+-free solution containing 2mm EGTA, but large positive membrane potentials (70 to 80 mV) were required in order to obtain open-state probabilities (P) above 0.1. Raising the free Ca2+ concentration in contact with the membrane inside ([Ca2+]i) to 1.5×10−7 m had little effect on the relationship between membrane potential andP. When [Ca2+]i was increased to 3×10−7 m and 6×10−7 m smaller potential changes were required to open the channels. Increasing [Ca2+]i further to 8×10−7 m again activated the channels, but the relationship between membrane potential andP was complex. Changing the membrane potential from −50 mV to +20 mV increasedP from near 0 to 0.6 but further polarization to +50 mV decreasedP to about 0.2. The pattern of voltage activation and inactivation was even more pronounced at [Ca2+]i=1 and 2 μm. In this situation a membrane potential change from −70 to +20 mV increasedP from near 0 to about 0.7 but further polarization to +80 mV reducedP to less than 0.1. The high-conductance K+ channel in rat pancreatic islet cells is remarkably sensitive to changes in [Ca2+]i within the range 0.1 to 1 μm which suggests a physiological role for this channel in regulating the membrane potential and Ca2+ influx through voltage-activated Ca2+ channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868748
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  • 6
    Electronic Resource
    Electronic Resource
    Interaction of diazoxide, tolbutamide and ATP4− on nucleotide-dependent K+ channels in an insulin-secreting cell line (1987)
    Springer
    The journal of membrane biology 99 (1987), S. 215-224 
    Details
    ISSN: 1432-1424
    Keywords: K+ channel ; ATP ; diazoxide ; tolbutamide ; RINm5F cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The single-channel current recording technique has been used to study the effects of diazoxide, tolbutamide and ATP, separately and combined, on the gating of nucleotide-regulated K+ channels in the insulin-secreting cell line RINm5F. The effects of diazoxide, tolbutamide and ATP4− were studied at the intracellular membrane surface, using, the open-cell membrane patch configuration. Alone diazoxide was found only inconsistently to evoke channel stimulation, 57% of all applications of the drug (72 times in 48 separate patches) having no effect at concentrations between 0.02 and 0.4mm. In the presence of ATP, however, diazoxide consistently evoked channel activation (seen 87 times in 49 patches, 95% of all applications). The interactions of diazoxide and ATP seemed competitive. Stimulation of channels by diazoxide in the presence of 1mm ATP was suppressed if the concentration of ATP was elevated to 2 or 5mm. In solutions in which Mg2+ had been chelated with EDTA, diazoxide failed to activate channels closed by 1mm ATP; however, this was not due to a direct effect on the channels caused by the absence of Mg2+, but could be explained by the enhanced ATP4− concentration after Mg2+ removal. When the total ATP concentration was lowered to give the same [ATP4−] in the absence of Mg2+ to that present in the control experiments, diazoxide was able to evoke full activation. Channel inhibition evoked by tolbutamide, 0.01 to 1.0mm, did not require the presence of either ATP or Mg2+. In the presence of ATP tolbutamide further reduced the number of channel openings. Diazoxide was able to compete with tolbutamide for control of channel activity, an effect that was augmented by the presence of ATP. In the presence of 0.1mm tolbutamide, diazoxide was unable to stimulate channel openings; however, if the dose of tolbutamide was lowered or ATP made available to the inside of the membrane, channel stimulation occurred.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01995702
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  • 7
    Electronic Resource
    Electronic Resource
    The gating of nucleotide-sensitive K+ channels in insulin-secreting cells can be modulated by changes in the ratio ATP4−/ADP3− and by nonhydrolyzable derivatives of both ATP and ADP (1988)
    Springer
    The journal of membrane biology 104 (1988), S. 165-177 
    Details
    ISSN: 1432-1424
    Keywords: K+ channel ; ATP ; ATP4− ; ADP3− ; RINm5F cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The31P-NMR technique has been used to assess the intracellular ratios and concentrations of mobile ATP and ADP and the intracellular pH in an insulin-secreting cell line, RINm5F. The single-channel current-recording technique has been used to investigate the effects of changes in the concentrations of ATP and ADP on the gating of nucleotide-dependent K+ channels. Adding ATP to the membrane inside closes these channels. However, in the continued presence of ATP adding ADP invariably leads to the reactivation of ATP-inhibited K+ channels, even at ATP4−/ADP3− concentration ratios greater than 7∶1. Interactions between ATP4− and ADP3− seem competitive. An increase in the concentration ratio ATP4−/ADP3− consistently evoked a decrease in the open-state probability of K+ channels; conversely a decrease in ATP4−/ADP3− increased the frequency of K+ channel opening events. Channel gating was also influenced by changes in the absolute concentrations of ATP4− and ADP3−, at constant free concentration ratios. ADP-evoked stimulation of ATP-inhibited channels did not result from phosphorylation of the channel, as ADP-β-S, a nonhydrolyzable analog of ADP, not only stimulated but enhanced ADP-induced activation of K+ channels, in the presence of ATP. Similarly, ADP was able to activate K+ channels in the presence of two nonhydrolyzable derivatives of ATP, AMP-PNP and βγmethylene ATP.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870928
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  • 8
    Electronic Resource
    Electronic Resource
    Control of K+ conductance by cholecystokinin and Ca2+ in single pancreatic acinar cells studied by the patch-clamp technique (1984)
    Springer
    The journal of membrane biology 79 (1984), S. 293-298 
    Details
    ISSN: 1432-1424
    Keywords: pancreatic acinar cells ; patch clamp ; whole cell recording ; single channel recording ; K+ channel ; Ca2− control ; cholecystokinin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The effect of cholecystokinin (CCK) and internal Ca2+ on outward K+ current in isolated pig pancreatic acinar cells has been investigated using the patch-clamp method for whole-cell current recording under voltage-clamp conditions. CCK (2 × 10−10 M) applied to the bath evoked a marked increase in the outward K+ current associated with depolarizing voltage steps, and this effect was fully reversible and acutely dependent on the presence of external Ca2+. When strongly buffered Ca2+-EGTA solutions were used inside the cells CCK failed to evoke an effect. Increasing the internal Ca2+ concentration ([Ca2+] i ) from 5 × 10−10 M to 10−7 and 5 × 10−7 M mimicked the effect of CCK. It would appear therefore that CCK controls K+ conductance in the acinar cells via changes in the internal free ionized Ca2+ concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871068
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