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  • 1
    Electronic Resource
    Electronic Resource
    The GTP-binding protein, G o 9 regulates neuronal calcium channels (1987)
    [s.l.] : Nature Publishing Group
    Nature 325 (1987), S. 445-447 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] ICa was determined in differentiated N x G cells by the whole-cell clamp technique15, using Ba2+ as charge carrier. Outward currents were minimized by replacing K+ with Cs+. On step-depolarizations from -40 to OmV, /Ca had a density of 11.5± 2.4(xAcm~2 (mean±s.d.; n=46); the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/325445a0
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  • 2
    Electronic Resource
    Electronic Resource
    On the mechanism of muscarinic inhibition of the cardiac Ca current (1986)
    Springer
    Pflügers Archiv 407 (1986), S. 182-189 
    Details
    ISSN: 1432-2013
    Keywords: Cardiac myocytes ; Ca current ; Muscarinic inhibition ; Adenylate cyclase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The mechanism of muscarinic inhibition of the Ca-current (I Ca) was studied in ventricular myocytes of guinea pig hearts and the following results were obtained. 1. Acetylcholine (ACh) in concentrations up to 10−4 M had little effect, if any, onI Ca in control cells. 2. ACh reduced the isoprenaline (ISP)-induced increase ofI Ca. The doseresponse-relation (ISP concentration vs.I Ca density) was shifted by ACh towards higher ISP concentrations. But both, at low and high ISP concentrations ACh had nor or little effect. 3. ACh was ineffective whenI Ca was increased by dialysing the cell with catalytic subunit of cAMP-dependent protein kinase or cAMP. 4. ACh reducedI Ca enhanced by isobutylmethylxanthine or by forskolin. 5. ACh did not depressI Ca when the cell was dialysed with the nonhydrolysable GTP-derivative, GMP-PNP. In this condition the β-adrenergic enhancement ofI Ca was also absent. 6. Pertussis toxin, which is known to inhibit the inhibitory transducerprotein (Ni), abolished the ACh response. We concluded from these results that ACh depressesI Ca by inhibiting, via Ni, the cAMP production.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00580674
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of a protein phosphatase inhibitor, okadaic acid, on membrane currents of isolated guinea-pig cardiac myocytes (1988)
    Springer
    Pflügers Archiv 412 (1988), S. 248-252 
    Details
    ISSN: 1432-2013
    Keywords: Cardiac muscle cell ; Whole-cell clamp recording ; Calcium current ; Protein phosphatase inhibitor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of a protein phosphatase inhibitor, okadaic acid (OA), were studied on membrane currents of isolated myocytes from guinea-pig cardiac ventricle. The whole-cell Ca2+ current (I Ca) was recorded as peak inward current in response to test pulse to O mV. Extracellular application of OA (5–100μM) produced an increase ofI Ca. The effect was markedly enhanced when the myocyte was pretreated with threshold concentrations of isoprenaline.I Ca was increased from 11.3±0.8μA cm−2 to 19.0±1.1μA cm−2 (n=4) by 5μM-OA in the presence of 1nM-isoprenaline. The delayed rectifier current was also slightly increased. Furthermore, the wash-out time of the β-adrenergic increase ofI Ca was markedly prolonged by OA. The β-adrenergic stimulation of cardiac Ca2+ current is thought to be mediated by cAMP-dependent phosphorylation. The present results strongly suggest that the effect of OA onI Ca is related to inhibition of endogenous protein phosphatase activity which is responsible for the dephosphorylation process. By the isotope method, the inhibitory effect of OA on different types of phosphatase was compared. OA had a relatively high specificity to type 1-, and type 2A-phosphatases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00582504
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  • 4
    Electronic Resource
    Electronic Resource
    On the mechanism of histamine induced enhancement of the cardiac Ca2+ current (1987)
    Springer
    Pflügers Archiv 410 (1987), S. 23-29 
    Details
    ISSN: 1432-2013
    Keywords: Histamine ; Ventricular myocytes ; Cacurrent ; cAMP-analogue ; GTP-analogues
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In guinea pig ventricular myocytes, the effect of histamine on the slow Ca2+ current (ICa) was studied and the following results were obtained: (1) Superfusion of cells with histamine resulted in a dose-dependent enhancement of the amplitude of ICa. The threshold concentration of histamine was 10−8 M, half maximal increase occurred at 3×10−7 M and maximal enhancement (about 3–4-fold) at 5×10−6 M. (2) The histamine effect was greatly reduced by the H2 antagonist cimetidine (10−5 M) but only slightly by the H1 antagonist diphenhydramine (10−5M). (3) Effects of isoprenaline (ISP) and histamine at maximal effective concentrations on ICa were not additive, suggesting that both agents use the same intracellular pathway. Intracellular infusion of a blocker of the cAMP-dependent protein kinase, Rp-cAMPS (10−4 M), prevented the histamine effect. (4) The involvement of GTP-dependent transducer proteins was studied by cell dialysis with several GTP derivatives. Intracellular application of the stable GDP-analogue, GDP-β-S, reduced the histamine effect on ICa, whereas the stable GTP analogue, GTP-γ-S, mimicked the histamine effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00581891
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  • 5
    Electronic Resource
    Electronic Resource
    Modulation of Ca current during the phosphorylation cycle in the guinea pig heart (1986)
    Springer
    Pflügers Archiv 407 (1986), S. 123-128 
    Details
    ISSN: 1432-2013
    Keywords: Guinea pig heart ; Ca current ; Phosphorylation cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The calcium current (I Ca) in the heart is increased by phosphorylation of a protein which is part of, or close to, the Ca channel. The phosphorylation is catalysed by cAMP-dependent protein kinase (cAMP-PK). The question whether dephosphorylated channels are available to open on depolarization was examined in ventricular myocytes of guinea pig by recording whole cellI Ca during dialysis with either regulatory (R) subunit of cAMP-PK or protein kinase inhibitor (PKI) or adenosine-5′-(γ-thio)-triphosphate (ATPγS). The following results were obtained: 1) R subunit reduced and PKI reversed the isoprenaline (ISP)-induced enhancement ofI Ca, suggesting their ability to inhibit cAMP-PK. 2) R subunit and PKI, however, reduced basal (i.e. non β-adrenergically stimulated)I Ca only by about 20%. 3) Dialysis with ATPγS resulted in a slow increase in basalI Ca, presumably due to dephosphorylation-resistant thiophosphorylation. 4) When, however, the cell was dialyzed with PKI the effect of ATPγS was almost completely suppressed, suggesting no detectable phosphorylation related to the channel activity in this condition. These results support the view that even in the dephosphorylated state Ca channels are available to open on depolarization and that phosphorylation by cAMP-PK increases the opening probability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00580662
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  • 6
    Electronic Resource
    Electronic Resource
    “Run-down” of the Ca current during long whole-cell recordings in guinea pig heart cells: role of phosphorylation and intracellular calcium (1988)
    Springer
    Pflügers Archiv 411 (1988), S. 353-360 
    Details
    ISSN: 1432-2013
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We examined by a statistical approach the decrease of the Ca current (“run-down”) during long-lasting recordings with the whole-cell patch-clamp technique in guinea pig ventricular myocytes. The results are as follows. (1) Run-down of the Ca current (I Ca) occurs in three phases (T1–T3). T1 (38±19 min,n=135) and T3 (35±17 min,n=23) are characterized by a slow rate of decay ofI Ca [90±20 and 60±20 nA·cm−2·min−1, respectively]. T1 and T3 are separated by T2 (6±4 min,n=135) during which the current decays quickly [1200±230 nA·cm−2·min−1]. Between the onsets of T1 and T3,I Ca decreases from 11±3 to 3.5±1 μA/cm2. (2) Normalized current-voltage relationship, reversal potential and voltage-dependencies of steady-state activation and inactivation ofI Ca are globally shifted toward more negative potentials during the run-down process by 10–15 mV. (3)I Ca3 measured during T3 retains the pharmacological properties (blockade by D600, NiCl2 and CoCl3, increase by isoprenaline and insensitivity to tetrodotoxin) of the originalI Ca. (4) Intracellular perfusion of the nonhydrolysable ATP analogue AMP-PNP does not prevent the occurrence of T2, suggesting that a phosphorylation-dephosphorylation process is not involved in the fast run-down ofI Ca. (5) With 0.1 mM EGTA in the pipette, addition of 3 mM ATP significantly prolongsI Ca survival. No improvements are obtained by increasing the ATP concentration to 10 mM or replacing ATP with creatine phosphate. With 3 mM ATP present, increasing the EGTA concentration to 10–20 mM doublesI Ca survival time. EGTA alone (10 mM) is less effective than the mixture 3 mM ATP-0.1 mM·EGTA. Intracellular perfusion with a cytoplasmic extract considerably prolongs T2 and the overallI Ca survival. (6) The results are consistent with the hypothesis that run-down ofI Ca can partially be explained by a rise in intracellular Ca concentration and a loss of high energy compounds. Beneficial effect of ATP might include an increased capability of the cells to either extrude or sequester intracellular Ca, and a protection against enzymatic proteolysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587713
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  • 7
    Electronic Resource
    Electronic Resource
    Regular and chaotic behaviour of cardiac cells stimulated at frequencies between 2 and 20 Hz (1989)
    Springer
    European biophysics journal 17 (1989), S. 273-280 
    Details
    ISSN: 1432-1017
    Keywords: Ventricular cardiocytes ; nonlinear dynamics ; chaos ; devil's staircase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract We measured the non-linear dynamics of cardiac action potentials by varying the stimulation frequency from 2 to 20 Hz and obtained the following results: (i) When the fast Na+ current initiated the action potentials (‘fast action potentials’) periodicity was maintained, i.e. the pattern of action potentials repeated after a finite number of stimuli. Chaotic sequences were absent. The transition from one sequence to the next occurred as a devil's staircase. (ii) When, however, the slow Ca2+ current initiated the action potentials (‘slow action potentials’), we observed chaos, i.e. fully irregular behaviour, as well as bifurcations. (iii) Our results confirm the supposition that the global dynamics of cardiac cells can be well described by simple one-dimensional maps which predict these two kinds of behaviour.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00254284
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  • 8
    Electronic Resource
    Electronic Resource
    Changes of membrane currents in cardiac cells induced by long whole-cell recordings and tolbutamide (1987)
    Springer
    Pflügers Archiv 409 (1987), S. 582-588 
    Details
    ISSN: 1432-2013
    Keywords: Cardiac myocytes ; Ca2+ current ; ATP-dependent K+ current ; Run-down ; ATP ; Tolbutamide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Single isolated myocytes were obtained from the ventricles of adult guinea pig hearts. The whole-cell recording configuration of the patch-clamp technique was used to measure membrane currents. A decrease (run-down) of the Ca2+ inward current and an increase of a time-independent K+ outward current were observed during long lasting (1–3 h) recordings. The time at which the outward current developed depended on the intracellular ATP concentration in the pipette, suggesting that this current is identical to the ATP-dependent K+ current described by Noma and Shibasaki (1985). However, the maximum outward current reached in the experiments was independent of the ATP concentration indicating a limited diffusion of ATP in the cell interior. In single-channel experiments on isolated patches of cell membrane and in whole-cell recordings the ATP-dependent K+ current could be blocked by the hypoglycaemic sulphonylurea tolbutamide. The IC50 of 0.38 mM was about 50 times higher than that reported for pancreatic β-cells (Trube et al. 1986). The Ca2+ inward current and the inwardly retifying K+ current were not affected by tolbutamide (3 mM).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00584657
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  • 9
    Electronic Resource
    Electronic Resource
    The protein-specific phosphatase 1 antagonizes the β-adrenergic increase of the cardiac Ca current (1986)
    Springer
    Pflügers Archiv 407 (1986), S. 461-463 
    Details
    ISSN: 1432-2013
    Keywords: Myocytes ; Ca current downregulation ; phosphatase-1
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In isolated ventricular cells from the adult guinea pig heart the slow Ca current was recorded during β-adrenergic stimulation and during cell dialysis with a protein-specific phosphatase-1 (PPase-1). The increase in the amplitude of ICa during bath application of isoprenaline (5×10−8M) could be completely reversed by dialysing the cell with 2 μM PPase-1. Lower enzyme concentrations produced smaller effects. The control amplitude of ICa was only little affected by dialysis with PPase-1. The result suggests 1) that PPase-1 is a likely candidate for the downregulation of Ca channels, 2) that Ca channels can open in the dephosphorylated state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00652635
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  • 10
    Electronic Resource
    Electronic Resource
    A possible physiological role of the Ca-dependent protease calpain and its inhibitor calpastatin on the Ca current in guinea pig myocytes (1988)
    Springer
    Pflügers Archiv 412 (1988), S. 554-556 
    Details
    ISSN: 1432-2013
    Keywords: Guinea pig myocytes ; Ca2+-current ; Rundown ; Calpain I/II ; Calpastatin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The decrease (‘run-down’) of the L-type Ca2+-current during long-lasting recordings with the whole-cell patch-clamp technique was examined in guinea pig ventricular myocytes. We have tested whether proteolysis is involved in the decay of the Ca2+-current by intracellular application of several concentrations of the Ca2+-dependent proteases calpain I and II, as well as their endogenous inhibitor calpastatin. The major finding was that calpain I and calpain II accelerated the Ca2+-current run-down in a concentration dependent manner, whereas calpastatin retarded it. These observations indicate that a proteolytic degradation of Ca2+-channels might be the reason for the run-down phenomenon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00582548
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