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1

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Calcium and Hormone Action (1994)

Petersen, O H ; Petersen, C C H ; Kasai, H

Palo Alto, Calif. : Annual Reviews

Annual Review of Physiology 56 (1994), S. 297-319

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ISSN: 0066-4278

Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff

Topics: Medicine , Biology

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1146/annurev.ph.56.030194.001501

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Activation of voltage-sensitive Ca2+ currents by vasopressin in an insulin-secreting cell line (1991)

Thorn, P. ; Petersen, O. H.

Springer

The journal of membrane biology 124 (1991), S. 63-71

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ISSN: 1432-1424

Keywords: Ca2+ channels ; vasopressin ; single-channel currents ; whole-cell current ; insulin secreting cell

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Chemistry and Pharmacology

Notes: Summary The effect of vasopressin on voltage-sensitive Ca2+ currents in the rat insulinoma cell line RINm5F has been investigated in patch-clamp whole-cell and single-channel current recording experiments. In the whole-cell recording configuration the dominant inward current in the presence of tetrodotoxin was noninactivating and had a high voltage threshold. This current was much enhanced when external Ca2+ was replaced by Ba2+ and was blocked by 1 μm nifedipine. It can therefore be classified as an L-current. Vasopressin enhanced the L-current without changing the voltage threshold of activation or the voltage at which the peak current was observed. Vasopressin effects were seen at concentrations as low as 0.01nm, and the maximal effect was observed at about 1nm. In higher concentrations the vasopressin effects were weaker, with effects at 50nm of about the same magnitude as at 0.01nm. In single-channel current recording experiments carried out with the cell-attached configuration there were no effects on single L-channel currents when vasopressin was added to the bath solution, but in experiments in which vasopressin (5nm) was infused into the patch pipette a marked increase in the apparent channel open state probability was observed. We conclude that vasopressin, a peptide that is known to markedly enhance glucose-evoked insulin secretion, stimulates opening of the voltage-sensitive Ca2+ channels in insulin-secreting cells.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01871365

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3

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Cytoplasmic Ca+ signals evoked by activation of cholecystokinin receptors: Ca2+-Dependent current recording in internally perfused pancreatic acinar cells (1991)

Wakui, M. ; Kase, H. ; Petersen, O. H.

Springer

The journal of membrane biology 124 (1991), S. 179-187

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ISSN: 1432-1424

Keywords: cholecytokinin ; Ca2+ signal ; caffeine ; heparin ; G protein

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Chemistry and Pharmacology

Notes: Summary The effects on the cytosolic Ca2+ concentration of activating cholecystokinin receptors on single mouse pancreatic acinar cells have been investigated using patch-clamp whole-cell recording of Ca2+-dependent Cl− current. We used the nonsulphated octapeptide of cholecystokinin (CCK8-NS) since the effects of even high concentrations were rapidly reversible which was not the case for the sulphated octapeptide. A submaximal concentration of CCK8-NS (10nm) evoked a current response consisting of short-lasting (a few seconds) spikes, and some of these spikes were seen to trigger larger and longer (about half a minute) current pulses. At a higher concentration (100nm) CCK8-NS evoked smooth and sustained responses. The effect of CCK8-NS was almost abolished when the internal perfusion solution contained a high concentration of the Ca2+ chelator EGTA (5mm). The responses evoked by CCK8-NS were independent of the presence of Ca2+ in the external solution at least for the first 5 min of stimulation. Internal perfusion with GTP-γ-S markedly potentiated the effect of CCK8-NS or at a higher concentration itself induced responses very similar to those normally evoked by CCK8-NS. Caffeine added to the external solution at a low concentration (0.2–1mm) enhanced weak CCK8-NS responses, whereas high caffeine concentrations always inhibited the CCK8-NS-evoked responses. These inhibitory caffeine effects were quickly reversible. Forskolin evoked a similar inhibitory effect. Intracellular heparin (200 μg/ml) infusion markedly inhibited the response to CCK8-NS stimulation. We conclude that the primary effect of activating CCK receptors is to induced inositoltrisphosphate (IP3) production. IP3 evokes a small and steady Ca2+ release, and this in turn evokes pulsatile release of a larger magnitude from a caffeine-sensitive Ca2+ pool. The action of CCK is thus very similar to that previously established for muscarinic receptor activation in the same cells. Nevertheless, the pattern of the cytosolic Ca2+ fluctuations are different, and the basic process of Ca2+-induced Ca2+ release and Ca2+ signal spreading must therefore be modulated by a messenger yet unknown.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01870462

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Stimulant-evoked depolarization and increase in [Ca2+] i in insulin-secreting cells is dependent on external Na+ (1990)

Dunne, M. J. ; Yule, D. I. ; Gallacher, D. V. ; [et al.]

Springer

The journal of membrane biology 113 (1990), S. 131-138

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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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5

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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)

Dunne, M. J. ; Yule, D. I. ; Gallacher, D. V. ; [et al.]

Springer

The journal of membrane biology 114 (1990), S. 53-60

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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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