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  • 1
    Electronic Resource
    Electronic Resource
    Dietary and Physiological Studies Involving Magnesium Homeostasis in the Heart (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 793 (1996), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1996.tb33544.x
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  • 2
    Electronic Resource
    Electronic Resource
    Inotropic responses of the isolated frog ventricle to serum (1984)
    Springer
    Pflügers Archiv 400 (1984), S. 205-207 
    Details
    ISSN: 1432-2013
    Keywords: contractile force ; frog ventricle ; calf-serum ; polypeptide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A study has been made of the effects of newborn calf-serum on the isolated frog ventricle. Preparations were superfused with solutions containing different concentrations of serum and the changes in contractility measured. Ordinary calf-serum evoked a dose-dependent increase in contractile force which was unaffected by adrenergic receptor antagonists (propranolol and phentolamine). Serum which was either used in growing HeLa cells or incubated with chymotrypsin failed to elicit a positive inotropic response. However, if prostaglandin-like materials were extracted from the serum then its ability to potentiate the twitch remained unaltered. These results suggest that the cardioactive-factor present in calf-serum is most probably related to a polypeptide, and possibly a growth factor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00585043
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of uridine triphosphate on contractility, cyclic nucleotide levels and membrane potential in the isolated frog ventricle (1981)
    Springer
    Pflügers Archiv 392 (1981), S. 1-6 
    Details
    ISSN: 1432-2013
    Keywords: Cyclic AMP ; Cyclic GMP ; Frog ventricle ; Action potential ; Contractility ; Uridine 5′-triphosphate ; Cyclic nucleotide ratio
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A study has been made of the effects of uridine 5′-triphosphate (UTP) on the isolated frog ventricle. Preparations were superfused with solutions containing different concentrations of UTP, and changes in contractility, cyclic nucleotide levels and membrane potential were measured. UTP produced a long lasting increase in isometric twitch tension, which was unaffected by adrenergic receptor antagonists (propranolol and phentolamine). The levels of adenosine 3′,5′-cyclic monophosphate (cyclic AMP) and guanosine 3′,5′-cyclic monophosphate (cyclic GMP) were measured at different times during exposure of the ventricle to 10−4 M UTP. The increase in the force of contraction was found to be accompanied by a rise in intracellular cyclic AMP. Cyclic GMP levels were seen to fall initially, but then to increase later, as both twitch and cyclic AMP started to decline. UTP also produced marked changes in the shape of the action potential; its duration and positive overshoot were both increased. The effects of UTP on twitch tension, cyclic nucleotide levels and action potential parameters were all dose-related. The change in contractility was found to be linearly related to (a) the ratio of the amount of cyclic AMP: cyclic GMP present in the fibres, and (b) to the increase in duration of the action potential. These results suggest that cyclic AMP, cyclic GMP and the availability of Ca2+ may all be involved in mediating the response to UTP.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00584573
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  • 4
    Electronic Resource
    Electronic Resource
    Stretch stimulates cyclic nucleotide metabolism in the isolated frog ventricle (1982)
    Springer
    Pflügers Archiv 395 (1982), S. 162-164 
    Details
    ISSN: 1432-2013
    Keywords: Stretch ; cyclic AMP ; cyclic GMP ; frog ventricle ; release
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract An investigation has been made of the effect of stretch on cyclic nucleotide metabolism. The levels of endogenous adénosine 3′,5′-cyclic monophosphate (cyclic AMP) and guanosine 3′,5′-cyclic monophosphate (cyclic GMP) were measured during different patterns of stretch and release. Stretch to Lmax produced a moderate increase in cyclic AMP and a proportionately greater increase in cyclic GMP; as a result, the ratio cyclic AMP: cyclic GMP fell to around 0.5 x control (unstretched) value. The effects of releasing previously stretched preparations resulted in a decrease in cyclic GMP levels. In contrast, the increase in cyclic AMP level following stretch was not affected by this procedure. Nevertheless, these effects together produced an increase in the ratio cyclic AMP: cyclic GMP, the magnitude of which increased linearly with the amplitude of release.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00584732
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  • 5
    Electronic Resource
    Electronic Resource
    The role of magnesium in regulating CCK-8-evoked secretory responses in the exocrine rat pancreas (1996)
    Springer
    Molecular and cellular biochemistry 154 (1996), S. 123-132 
    Details
    ISSN: 1573-4919
    Keywords: rat pancreas ; cholecystokinin-octapeptide ; magnesium ; calcium ; secretion ; cyclic AMP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract This study investigates the effect of magnesium (Mg2+) on the secretory responses and the mobilization of calcium (Ca2+) and Mg2+ evoked by cholecystokinin-octapeptide (CCK-8) in the exocrine rat pancreas. In the isolated intact perfused pancreas CCK-8 (10−10 M) produced marked increases in juice flow and total protein output in zero and normal (1.1 mM) extracellular Mg2+ [Mg2+]o compared to a much reduced secretory response in elevated (5 mM and 10 mM) [Mg2+]o Similar effects of perturbation of [Mg2+]o on amylase secretion and 45Ca2+ uptake (influx) were obtained in isolated pancreatic segments. In pancreatic acinar cells loaded with the fluorescent bioprobe fura-2 acetomethylester (AM), CCK-8 evoked marked increases in cytosolic free Ca2+ concentration [Ca2+]i in zero and normal [Mg2+]o compared to a much reduced response in elevated [Mg2+]o Pretreatment of acinar cells with either dibutyryl cyclic AMP (DB2 cAMP) or forskolin had no effect on the CCK-8 induced changes in [Ca2+]i. In magfura-2-loaded acinar cells CCK-8 (10−8 M) stimulated an initial transient rise in intracellular free Mg2+ concentration [Mg2+]i followed by a more prolonged and sustained decrease. This response was abolished when sodium Na+ was replaced with N-methyl-D-glucamine (NMDG). Incubation of acinar cells with 10 mM Mg2+ resulted in an elevation in [Mg2+]i. Upon stimulation with CCK-8, [Mg2+]i. decreased only slightly compared with the response obtained in normal [Mg2+]o. CCK-8 caused a net efflux of Mg2+ in pancreatic segments; this effect was abolished when extracellular sodium [Na+]o was replaced with either NMDG or choline. The results indicate that Mg2+ can regulate CCK-8-evoked secretory responses in the exocrine pancreas possibly via Ca2+ mobilization. Moreover, the movement of Mg2+ in pancreatic acinar cells is dependent upon extracellular Na+.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00226780
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  • 6
    Electronic Resource
    Electronic Resource
    Dietary and physiological studies to investigate the relationship between calcium and magnesium signalling in the mammalian myocardium (1997)
    Springer
    Molecular and cellular biochemistry 176 (1997), S. 127-134 
    Details
    ISSN: 1573-4919
    Keywords: heart ; calcium ; magnesium ; contractility ; dietary ; L-type calcium current
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract This study employs both dietary and physiological studies to investigate the relationship between calcium (Ca2+) and magnesium (Mg2+) signalling in the mammalian myocardium. Rats maintained on a low Mg2+ diet (LMD; 39 mg Kg-1 Mg2+ in food) consumed less food and grew more slowly than control rats fed on a control Mg2+ diet (CMD; 500 mg Kg-1 Mg2+ in food). The Mg2+ contents of the heart and plasma were 85 ± 3% and 34 ± 6.5%, respectively relative to the control group. In contrast, Ca2+ contents in the heart and plasma were 177 ± 5% and 95 ± 3%. The levels of potassium (K+) was raised in the plasma (129 ± 16%) and slightly decreased in the heart (88 ± 6%) compared to CMD. Similarly, sodium (Na+) contents were slightly higher in the heart and lowered in the plasma of low Mg2+ diet rats compared to control Mg2+ diet rat. Perfusion of the isolated Langendorff's rat heart with a physiological salt solution containing low concentrations (0-0.6 mM) of extracellular magnesium [Mg2+]0 resulted in a small transient increase in the amplitude of contraction compared to control [Mg2+]0 (1.2 mM). In contrast, elevated [Mg2+]0 (2-7.2 mM) caused a marked and progressive decrease in contractile force compared to control. In isolated ventricular myocytes the L-type Ca2+ current (ICa,L was significantly (p 〈 0.001) attenuated in cells dialysed with 7.1 mM Mg2+ compared to cells dialysed with 2.9 µM Mg2+. The results indicate that hypomagnesemia is associated with decrease levels of Mg2+ and elevated levels of Ca2+ in the heart and moreover, internal Mg2+ is able to modulate the Ca2+ current through the L-type Ca2+ channel which in turn may be involved with the regulation of contractile force in the heart.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006839315221
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  • 7
    Electronic Resource
    Electronic Resource
    Early postnatal changes in sarcoplasmic reticulum calcium transport function in spontaneously hypertensive rats (1996)
    Springer
    Molecular and cellular biochemistry 163-164 (1996), S. 57-66 
    Details
    ISSN: 1573-4919
    Keywords: heart ; postnatal development ; sarcoplasmic reticulum ; phospholamban ; calcium transport ; spontaneously hypertensive rats ; growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract This comparative study investigates the relationship between sarcoplasmic reticulum (SR) calcium(Ca2+)-ATPase transport activity and phospholamban (PLB) phosphorylation in whole cardiac homogenates of spo`ntaneously hypertensive rats (SHR) and their parent, normotensive Wistar Kyoto (WKY) strain during early postnatal development at days 1, 3, 6, 12 and at day 40 to ascertain any difference in SR Ca2+ handling before the onset of hypertension. At day 1, the rate of homogenate oxalate-supported Ca2+ uptake was significantly higher in SHR than in WKY (0.25 ± 0.02 vs 0.12 ± 0.01 nmoles Ca2+/mg wet ventricular weight/min, respectively; p 〈 0.001). This interstrain difference disappeared with further developmental increase in SR Ca2+ transport. Western Blot analysis and a semiquantitative ELISA did not reveal any difference in the amount of immunoreactive PLB (per mg of total tissue protein) between strains at any of the ages studied. In addition, levels of phosphorylated PLB formed in vitro in the presence of radiolabelled ATP and catalytic (C) subunit of protein kinase A did not differ between SHR and WKY at days 1, 3, 6 and 12. At day 40, C subunit-catalyzed formation of 32P-PLB was reduced by 66% (p 〈 0.001) in SHR when compared to age-matched WKY In the early postnatal period between day 1 and 12 SR Ca2+-transport values were linearly related to the respective 32P-PLB levels of both SHR and WKY rats. The results indicate that cardiac SR of SHR can sequester Ca2+ at a much higher rate immediately after birth compared to WKY rats. The disappearance of this interstrain difference with further development suggests that some endogenous neuroendocrine or nutritional factor(s) from the hypertensive mother may exert an influence upon the developing heart in utero resulting in a transiently advanced maturation of the SR Ca2+ transport function in SHR pups at the time of birth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00408641
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of dephostatin on intracellular free calcium concentration and amylase secretion in isolated rat pancreatic acinar cells (2000)
    Springer
    Molecular and cellular biochemistry 205 (2000), S. 163-169 
    Details
    ISSN: 1573-4919
    Keywords: calcium ; pancreatic acinar cell ; dephostatin ; cholecystokinin ; amylase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract This study investigates the effects of dephostatin, a new tyrosine phosphatase inhibitor, on intracellular free calcium concentration ([Ca2+]i) and amylase secretion in collagenase dispersed rat pancreatic acinar cells. Dephostatin evoked a sustained elevation in [Ca2+]i by mobilizing calcium from intracellular calcium stores in either the absence of extracellular calcium or the presence of lanthanium chloride (LaCl3). Pretreatment of acinar cells with dephostatin prevented cholecystokinin-octapeptide (CCK-8)-induced signal of [Ca2+]i and inhibited the oscillatory pattern initiated by aluminium fluoride (AlF- 4), whereas co-incubation with CCK-8 enhances the plateau phase of calcium response to CCK-8 without modifying the transient calcium spike. The effects of dephostatin on calcium mobilization were reversed by the presence of the sulfhydryl reducing agent, dithiothreitol. Stimulation of acinar cells with thapsigargin in the absence of extracellular Ca2+ resulted in a transient rise in [Ca2+]i . Application of dephostatin in the continuous presence of thapsigargin caused a small but sustained elevation in [Ca2+]i . These results suggest that dephostatin can mobilize Ca2+ from both a thapsigargin-sensitive and thapsigargin-insensitive intracellular stores in pancreatic acinar cells. In addition, dephostatin can stimulate the release of amylase from pancreatic acinar cells and moreover, reduce the secretory response to CCK-8. The results indicate that dephostatin can release calcium from intracellular calcium pools and consequently induces amylase secretion in pancreatic acinar cells. These effects are likely due to the oxidizing effects of this compound.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007086401390
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  • 9
    Electronic Resource
    Electronic Resource
    Second messenger role of magnesium in pancreatic acinar cells of the rat (1995)
    Springer
    Molecular and cellular biochemistry 149-150 (1995), S. 175-182 
    Details
    ISSN: 1573-4919
    Keywords: rat pancreas ; cholecystokinin ; magnesium ; calcium ; acetylcholine ; amylase secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Application of either acetylcholine (ACh, 10−5 M) or cholecystokininoctapeptide (CCK-8, 10−8 M) to the isolated rat pancreas elicited large increases in amylase secretion, radiolabelled45Ca2+ influx and cytosolic free calcium [Ca2+]i levels in zero and normal (1.1 mM) extracellular magnesium [Mg2+]o. Elevated [Mg2+]o significantly (p〈0.001) reduced the secretagogueevoked secretory responses and Ca2+ mobilisation. Stimulation of pancreatic segments with either ACh (10−5 and 10−6 M) or CCK-8 (10−8 and 10−10 M) resulted in marked elevation in Mg2+ concentration in effluent samples (net efflux). On removal of either ACh or CCK-8, Mg2+ concentration returned to resting level. In pancreatic acinar cells loaded the flourescent dye magfura, ACh and CCK-8 evoked marked reduction in cytosolic free Mg2+ concentration [Mg2+]i compared to the resting value of 0.82±0.03 mM (n=50) in normal medium in the absence of secretagogues. In elevated [Mg2+]o (10 mM) medium, [Mg2+]i rises to 0.98±0.04 mM (n=6). Addition of CCK-8 led to only a small reduction in [Mg2+ i in elevated [Mg2+]o. In Mg2+ loaded pancreatic acinar cells, Mg2+ is released in a time dependent manner and this efflux of Mg2+ was sensitive to sodium, extracellular amiloride (1 mM), dinitrophenol (10 mM) and lidocaine (1 mM). The results indicate that Mg2+ is acting as an intracellular messenger to regulate the mobilisation of Ca2+ which in turn mediates enzyme secretion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01076575
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  • 10
    Electronic Resource
    Electronic Resource
    l-Alanine andl-phenylalanine activate Na+ and K+ conductance pathways in the exocrine mouse pancreas (1984)
    Springer
    Pflügers Archiv 402 (1984), S. 176-184 
    Details
    ISSN: 1432-2013
    Keywords: Amino acids ; Membrane potential ; Membrane current ; Amylase secretion ; 45Ca and86Rb efflux ; Mouse pancreas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of some amino acids,l-alanine,l-phenylalanine,dl-alanine,d-alanine and β-alanine on membrane potential, membrane current, amylase secretion and45Ca and86Rb fractional efflux in isolated mouse pancreatic segments were investigated. A two micro-electrode voltage clamp technique was applied to study the effects of the amino acids on membrane current. The amino acids evoked dose-dependent (0.05–0.5 mmole) and reversible membrane depolarization and increases in membrane current. The relative potencies of the actions of the amino acids were:l-alanine〉dl-alanine〉l-phenylalanine〉d-alanine〉β-alanine. A more detailed study of the action ofl-alanine showed that the relationship between thel-alanine-evoked membrane current and membrane potential was virtually linear with reversal of current polarity being observed at a membrane potential of about +30 mV. While thel-alanine-induced increase in membrane conductance was dose-dependent, the reversal potential (E l-ala) was independent of thel-alanine concentration used. Replacement of the normal Na-rich superfusion fluid by a low Na solution (5 mM) markedly reduced thel-alanine-elicited inward current at the normal resting potential. Thel-alanine-evoked conductance increase was also reduced in low Na solution and the E l-ala was close to 0 mV. During the exposure of pancreatic segments to Cl free solution (sulphate substitution) E l-ala was about 12 mV more positive (+43.7±0.8 mV) than during exposure to control solution (+31.5±1.0 mV). Calculations based on the Goldman-Hodgkin-Katz equations taking into account the values of E l-ala in the different ionic situations, indicate that the relative permeability of the ionic pathway opened up in the presence ofl-alanine isP Na/P Cl/P K=7.5/1.5/1.0 The pathway is therefore Na selective, but with some leak permeability for Cl and K. In the physiological range of membrane potentials (−15 to −40 mV) the current evoked byl-alanine is virtually entirely carried by Na. Measurements of amylase secretion and45Ca fractional efflux show that none of the amino acids (all at 10 mM concentrations) had significant effect whereas pentagastrin (Pn; 10−6 M) elicited marked increases in amylase output and45Ca release. Both pentagastrin andl-alanine stimulated the release of86Rb from prelabelled tissue whereasdl-alanine,l-phenylalanine,d-alanine and β-alanine had little or no effect. The present results indicate that although the amino acids have no effect on either amylase secretion or calcium metabolism, they nevertheless open conductance pathways in the acinar plasma membrane mainly permeable to Na.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00583332
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