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  • 1
    Electronic Resource
    Electronic Resource
    Verapamil, a phenylalkylamine Ca2 + channel blocker, inhibits ATP-sensitive K + channels in insulin-secreting cells from rats (1997)
    Springer
    Diabetologia 40 (1997), S. 1403-1410 
    Details
    ISSN: 1432-0428
    Keywords: Keywords Verapamil ; ATP-sensitive K + channel ; rat pancreatic beta cells ; insulin release.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Radioisotopic and electrophysiological techniques were used to assess the effects of verapamil, a phenylalkylamine Ca2 + channel blocker, on K + permeability of insulin-secreting cells. Verapamil provoked a concentration-dependent inhibition of 86Rb (42K substitute) outflow from prelabelled and perifused rat pancreatic islets. This property appears to be inherent to the phenylalkylamine Ca2 + channel blockers since gallopamil, a methoxyderivative of verapamil, but not nifedipine, a 1,4-dihydropyridine Ca2 + channel blocker, inhibited 86Rb outflow. The experimental data further revealed that verapamil interacted with a Ca2 + -independent, glucose- and glibenclamide-sensitive modality of 86Rb extrusion. Moreover, verapamil prevented the increase in 86Rb outflow brought about by BPDZ 44; a potent activator of the ATP-sensitive K + channel. Single-channel current recordings by the patch clamp technique confirmed that verapamil elicited a dose-dependent inhibition of the ATP-dependent K + channel. Lastly, under experimental conditions in which verapamil clearly inhibited the ATP-sensitive K + channels, the drug did not affect 45Ca outflow, the cytosolic free Ca2 + concentration or insulin release. It is concluded that the Ca2 + entry blocker verapamil inhibits ATP-sensitive K + channels in pancreatic beta cells. This effect was not associated with stimulation of insulin release [Diabetologia (1997) 40: 1403–1410].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001250050842
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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    ATP-sensitive inward rectifier and voltage- and calcium-activated K+ channels in cultured pancreatic islet cells (1985)
    Springer
    The journal of membrane biology 88 (1985), S. 165-172 
    Details
    ISSN: 1432-1424
    Keywords: islet ; K+ channels ; ATP ; Ca2+ ; patch-clamp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary K+ channels in cultured rat pancreatic islet cells have been studied using patch-clamp single-channel recording techniques in cell-attached and excised inside-out and outside-out membrane patches. Three different K+-selective channels have been found. Two inward rectifier K+ channels with slope conductances of about 4 and 17 pS recorded under quasi-physiological cation gradients (Na+ outside, K+ inside) and maximal conductances recorded in symmetrical K+-rich solutions of about 30 and 75 pS, respectively. A voltage- and calcium-activated K− channel was recorded with a slope conductance of about 90 pS under the same conditions and a maximal conductance recorded in symmetrical K+-rich solutions of about 250 pS. Single-channel current recording in the cell-attached conformation revealed a continuous low level of activity in an apparently small number of both the inward rectifier K+ channels. But when membrane patches were excised from the intact cell a much larger number of inward rectifier K+ channels became transiently activated before showing an irreversible decline. In excised patches opening and closing of both the inward rectifier K+ channels were unaffected by voltage, internal Ca2+ or externally applied tetraethyl-ammonium (TEA) but the probability of opening of both inward rectifier K+ channels was reduced by internally applied 1–5mm adenosine-5′-triphosphate (ATP). The large K+ channel was not operational in cell-attached membrane patches, but in excised patches it could be activated at negative membrane potentials by 10−7 to 10−6 m internal Ca2+ and blocked by 5–10mm external TEA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868430
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Stimulant-evoked depolarization and increase in [Ca2+] i in insulin-secreting cells is dependent on external Na+ (1990)
    Springer
    The journal of membrane biology 113 (1990), S. 131-138 
    Details
    ISSN: 1432-1424
    Keywords: patch clamp ; [Ca2+] i ; Na+ dependency ; RINm5F cell ; fura-2 ; whole cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The patch-clamp technique and measurements of single cell [Ca2+] i have been used to investigate the importance of extracellular Na+ for carbohydrate-induced stimulation of RINm5F insulin-secreting cells. Using patch-clamp whole-cell (current-clamp) recordings the average cellular transmembrane potential was estimated to be −60±1 mV (n=83) and the average basal [Ca2+] i 102±6nm (n=37). When challenged with either glucose (2.5–10mm) ord-glyceraldehyde (10mm) the cells depolarized, which led to the initiation of Ca2+ spike potentials and a sharp rise in [Ca2+] i . Similar effects were also observed with the sulphonylurea compound tolbutamide (0.01–0.1mm). Both the generation of the spike potentials and the increase in [Ca2+] i were abolished when Ca2+ was removed from the bathing media. When all external Na+ was replaced with N-methyl-d-glucamine, in the continued presence of either glucose,d-glyceraldehyde or tolbutamide, a membrane repolarization resulted, which terminated Ca2+ spike potentials and attenuated the rise in [Ca2+] i . Tetrodotoxin (TTX) (1–2 μm) was also found to both repolarize the membrane and abolish secretagogue-induced rises in [Ca2+] i .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01872887
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  • 6
    Electronic Resource
    Electronic Resource
    Comparative study of the effects of cromakalim (BRL 34915) and diazoxide on membrane potential, [Ca2+] i and ATP-sensitive potassium currents in insulin-secreting cells (1990)
    Springer
    The journal of membrane biology 114 (1990), S. 53-60 
    Details
    ISSN: 1432-1424
    Keywords: patch-clamp ; fura-2 ; KATP channels ; [Ca2+] i ; insulin-secreting cell ; RINm5F cell ; diazoxide ; cromakalim (BRL 34915) ; tolbutamide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Patch-clamp and single cell [Ca2+] i measurements have been used to investigate the effects of the potassium channel modulators cromakalim, diazoxide and tolbutamide on the insulin-secreting cell line RINm5F. In intact cells, with an average cellular transmembrane potential of −62±2 mV (n=42) and an average basal [Ca2+] i of 102±6nm (n=37), glucose (2.5–10mm): (i) depolarized the membrane, through a decrease in the outward KATP current, (ii) evoked Ca2+ spike potentials, and (iii) caused a sharp rise in [Ca2+] i . In the continued presence of glucose both cromakalim (100–200 μm) and diazoxide (100 μm) repolarized the membrane, terminated Ca2+ spike potentials and attenuated the secretagogue-induced rise in [Ca2+] i . In whole cells (voltage-clamp records) and excised outside-out membrane patches, both cromakalim and diazoxide enhanced the current by opening ATP-sensitive K+ channels. Diazoxide was consistently found to be more potent than cromakalim. Tolbutamide, a specific inhibitor of ATP-sensitive K+ channels, reversed the effects of cromakalim on membrane potential and KATP currents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869384
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  • 7
    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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  • 8
    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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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    Regulation of Intracellular Ca2+ in Response to Muscarinic and Glutamate Receptor Agonists During the Differentiation of NTERA2 Human Embryonal Carcinoma Cells into Neurons (1996)
    Oxford, UK : Blackwell Publishing Ltd
    European journal of neuroscience 8 (1996), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Single cell microfluorimetry was used to study intracellular calcium ion signals ([Ca2+]i) evoked by acetylcholine (ACh), glutamate receptor agonists and by KCI-induced membrane depolarization, during neuronal differentiation of the human embryonal carcinoma (EC) cell line, NTERA2. In undifferentiated NTERA2 EC cells, [Ca2+]i) was elevated in response to ACh, but not to the glutamate receptor agonists NMDA, kainate or AMPA. The ACh-induced rise in [Ca2+]i) was dependent upon both Ca2+ influx and Ca2+ mobilization from cytoplasmic calcium stores. Three other human EC cell lines responded similarly to ACh but not to glutamate or KCI-induced depolarization. In neurons derived from NTERA2 cells by retinoic acid induction, [Ca2+]i) signals were evoked by ACh, NMDA, kainate and by an elevation of the extracellular KCI concentration. As in undifferentiated EC cells, the ACh-mediated increases in [Ca2+li were governed by both Ca2+ influx and Ca2+ mobilization. In contrast, the effects of NMDA, kainate and KCI did not involve intracellular Ca2+ mobilization. The appearance of glutamate and KCI responsiveness was not detected in non-neuronal differentiated derivatives of NTERA2 cells. Using a number of pharmacologically defined muscarinic receptor antagonists we found that NTERA2 EC cells express M1, M3, M4 and possibly M5 receptor subtypes linked to changes in [Ca2+]i), whilst only M3 and M5 are present in NTERA2-derived neurons. The results were supported by PCR analysis of the muscarinic mRNA species expressed in the cells. The data demonstrate that differentiation of NTERA2 EC cells into neurons involves the induction of functional glutamate receptors coupled to rises in [Ca2+]i), and changes in the expression of muscarinic ACh receptor subtypes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-9568.1996.tb01263.x
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