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  • 1985-1989  (8)
  • fluid secretion  (5)
  • insulin  (2)
  • genetics
  • 1
    Electronic Resource
    Electronic Resource
    Evidence for a Na+/K+/Cl− cotransport system in basolateral membrane vesicles from the rabbit parotid (1986)
    Springer
    The journal of membrane biology 94 (1986), S. 143-152 
    Details
    ISSN: 1432-1424
    Keywords: fluid secretion ; exocrine gland ; chloride transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Sodium (22Na) transport was studied in a basolateral membrane vesicle preparation from rabbit parotid. Sodium uptake was markedly dependent on the presence of both K+ and Cl− in the extravesicular medium, being reduced 5 times when K+ was replaced by a nonphysiologic cation and 10 times when Cl− was replaced by a nonphysiologic anion. Sodium uptake was stimulated by gradients of either K+ or Cl− (relative to nongradient conditions) and could be driven against a sodium concentration gradient by a KCl gradient. No effect of membrane potentials on KCl-dependent sodium flux could be detected, indicating that this is an electroneutral process. A KCl-dependent component of sodium flux could also be demonstrated under equuilibrium exchange conditions, indicating a direct effect of K+ and Cl− on the sodium transport pathway. KCl-dependent sodium uptake exhibited a hyperbolic dependence on sodium concentration consistent with the existence of a single-transport system withK m =3.2mm at 80mm KCl and 23°C. Furosemide inhibited this transporter withK 0.5=2×10−4 m (23°C). When sodium uptake was measured as a function of potassium and chloride concentrations a hyperbolic dependence on [K] (Hill coefficient =1.31±0.07) were observed, consistent with a Na/K/Cl stoichiometry of 1∶1∶2. Taken together these data provide strong evidence for the electroneutral coupling of sodium and KCl movements in this preparation and strongly support the hypothesis that a Na+/K+/Cl− cotransport system thought to be associated with transepithelial chloride and water movements in many exocrine glands is present in the parotid acinar basolateral membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871194
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  • 2
    Electronic Resource
    Electronic Resource
    Analysis of the HepG2/erythrocyte glucose transporter locus in a family with Type 2 (non-insulin-dependent) diabetes and obesity (1989)
    Springer
    Diabetologia 32 (1989), S. 266-269 
    Details
    ISSN: 1432-0428
    Keywords: Type 2 (non-insulin-dependent) diabetes ; genetics ; linkage ; glucose transporter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A recent report has shown an association between a specific Xba1 restriction fragment of the human HepG2-Erythrocyte glucose transporter gene and Type 2 (non-insulin dependent) diabetes. To further examine the significance of this finding we have studied Type 2 diabetic pedigrees for linkage between the Xba1 alleles of this glucose transporter gene and diabetes. One large pedigree, in which the diabetic phenotype was associated with obesity and insulin resistance, was informative. In this family the disease did not co-segregate with the glucose transporter locus. Formal linkage analysis was performed assuming autosomal dominant inheritance with age-dependent penetrance. At putative gene frequencies of 0.01 and 0.001 the logarithin of the odds for linkage versus non-linkage at a recombination fraction of 0.001 was −1.84 and −3.32 respectively (a value of 〈-2 indicates definite non-linkage). Genetic variations in the HepG2-Erythrocyte glucose transporter gene are unlikely to be responsible for the development of diabetes in this pedigree.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00285296
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  • 3
    Electronic Resource
    Electronic Resource
    Sulphonylurea therapy doubles B-cell response to glucose in Type 2 diabetic patients (1985)
    Springer
    Diabetologia 28 (1985), S. 809-814 
    Details
    ISSN: 1432-0428
    Keywords: Sulphonylureas ; insulin ; C-peptide ; insulin resistance ; hyperglycaemic clamp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effect of sulphonylurea therapy for 3 weeks on glucose-stimulated insulin secretion and insulin resistance was studied in Type 2 diabetic patients. The fasting plasma insulin and C-peptide concentrations on diet alone were compared with each subject's fasting concentrations on sulphonylurea treatment at a lower fasting plasma glucose and at the original diet-alone glycaemic level obtained by the hyperglycaemic clamp technique. At this isoglycaemic level (mean 11 mmol/l), plasma insulin levels increased from 6.9 mU/l on diet alone to 12.1 mU/l on sulphonylurea treatment (p〈0.01). The subjects were also studied by the hyperglycaemic clamp technique at mean glycaemic levels of 13 mmol/l before and after sulphonylurea treatment; the incremental insulin response was similarly enhanced from 7.6±3.5 to 13.7±6.9 mU/l (p〈0.02) respectively. Sulphonylureas appear to reduce glycaemia by enhancing B-cell function two-fold. In the patients studied this was from approximately 21% to 37% of a normal response. Insulin resistance assessed by the same hyperglycaemic clamps as endogenous plasma insulin concentrations divided by glucose infusion rates was unchanged by sulphonylurea therapy (mean 4.37 compared to 4.40 mU. 1−1·mg−1·kg·min on diet alone).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00291069
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  • 4
    Electronic Resource
    Electronic Resource
    Homeostasis model assessment: insulin resistance and β-cell function from fasting plasma glucose and insulin concentrations in man (1985)
    Springer
    Diabetologia 28 (1985), S. 412-419 
    Details
    ISSN: 1432-0428
    Keywords: β-cell function ; insulin resistance ; mathematical model ; intravenous glucose tolerance test ; glucose clamp ; insulin receptors ; Type 2 diabetes ; insulin ; glucose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The steady-state basal plasma glucose and insulin concentrations are determined by their interaction in a feedback loop. A computer-solved model has been used to predict the homeostatic concentrations which arise from varying degrees of β-cell deficiency and insulin resistance. Comparison of a patient's fasting values with the model's predictions allows a quantitative assessment of the contributions of insulin resistance and deficient β-cell function to the fasting hyperglycaemia (homeostasis model assessment, HOMA). The accuracy and precision of the estimate have been determined by comparison with independent measures of insulin resistance and β-cell function using hyperglycaemic and euglycaemic clamps and an intravenous glucose tolerance test. The estimate of insulin resistance obtained by homeostasis model assessment correlated with estimates obtained by use of the euglycaemic clamp (Rs = 0.88, p 〈 0.0001), the fasting insulin concentration (Rs = 0.81, p 〈 0.0001), and the hyperglycaemic clamp, (Rs = 0.69, p 〈 0.01). There was no correlation with any aspect of insulin-receptor binding. The estimate of deficient β-cell function obtained by homeostasis model assessment correlated with that derived using the hyperglycaemic clamp (Rs = 0.61, p 〈 0.01) and with the estimate from the intravenous glucose tolerance test (Rs = 0.64, p 〈 0.05). The low precision of the estimates from the model (coefficients of variation: 31% for insulin resistance and 32% for β-cell deficit) limits its use, but the correlation of the model's estimates with patient data accords with the hypothesis that basal glucose and insulin interactions are largely determined by a simple feed back loop.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00280883
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  • 5
    Electronic Resource
    Electronic Resource
    Agonist-induced activation of Na+/H+ exchange in rat parotid acinar cells (1989)
    Springer
    The journal of membrane biology 111 (1989), S. 191-198 
    Details
    ISSN: 1432-1424
    Keywords: exocrine gland ; pH regulation ; Na+/H+ exchange ; fluid secretion ; muscarinic agonist
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The present studies were designed to test our previous suggestion that Na+/H+ exchange was activated by muscarinic stimulation of rat parotid acinar cells. Consistent with this hypothesis, we demonstrate here that intact rat parotid acini stimulated with the muscarinic agonist carbachol in HCO 3 − -free medium show an enhanced recovery from an acute acid load as compared to similarly challenged untreated preparations. Amiloride-sensitive22Na uptake, due to Na+/H+ exchange, was also studied in plasma membrane vesicles prepared from rat parotid acini pretreated with carbachol. This uptake was stimulated twofold relative to that observed in vesicles from control (untreated) acini. This stimulation was time dependent, requiring ∼15 min of acinar incubation with carbachol to reach completion, and ws blocked by the presence of the muscarinic antagonist atropine (2×10−5 m) in the pretreatment medium. The effect of carbachol was dose dependent withK 0.5∼3×10−6 m. Stimulation of the exchanger was also seen in vesicles prepared from acini pretreated with the α-adrenergic agonist epinephrine, but not with the β-adrenergic agonist isoproterenol, or with substance P. Kinetic analysis indicated that the stimulation induced by carbachol was due to an alkaline shift in the pH responsiveness of the exchanger in addition to an increasedapparent transport capacity. Taken together with previous results from this and other laboratories, these results strongly suggest that the Na+/H+ exchanger and its regulation are intimately involved in the fluidsecretory response of the rat parotid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871782
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  • 6
    Electronic Resource
    Electronic Resource
    Inactivation of the rabbit parotid Na/K/Cl cotransporter by N-ethylmaleimide (1989)
    Springer
    The journal of membrane biology 112 (1989), S. 51-58 
    Details
    ISSN: 1432-1424
    Keywords: loop diuretics ; exocrine gland ; fluid secretion ; parotid ; acinar cell ; ion transport ; chloride secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The inactivation of the rabbit parotid Na/K/Cl cotransporter by the irreversible sulfhydryl reagent N-ethylmaleimide (NEM) is studied by monitoring its effect on high affinity bumetanide binding to the carrier. NEM reduces the number of bumetanide binding sites with no significant change in the affinity of those remaining. NEM also reduces KCl-dependent22Na flux via the cotransporter by the same factor as the reduction in bumetanide binding sites. Both bumetanide and its analogue furosemide can protect against the effect of NEM. The concentration range over which this protection occurs is in good agreement with affinities of these two compounds for the high affinity bumetanide binding site (2.6 and 85 μm, respectively), indicating an association of this site with the site of action of NEM. Also consistent with this hypothesis are the observations that (i) sodium and potassium, both of which are required for high affinity bumetanide binding, increase the rate of inactivation of binding by NEM and (ii) chloride, at concentrations previously shown to competitively inhibit bumetanide binding, protects the cotransporter against NEM. The effects of NEM on bumetanide binding are mimicked by another highly specific sulfhydryl reagent, methyl methanethiolsulfonate. The apparent rate constant for inactivation of high affinity bumetanide binding by NEM is a hyperbolic function of NEM concentration consistent with a model in which the inactivation reaction is first order in [NEM] and proceeds through an intermediate adsorptive complex. The data indicate that the presence of a reduced sulfhydryl group at or closely related to the bumetanide binding site is essential for the operation of the parotid Na/K/Cl cotransporter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871163
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  • 7
    Electronic Resource
    Electronic Resource
    Coupled Na+/H+ exchange in rat parotid basolateral membrane vesicles (1988)
    Springer
    The journal of membrane biology 102 (1988), S. 247-254 
    Details
    ISSN: 1432-1424
    Keywords: exocrine gland ; parotid ; acinar cell ; ion transport ; fluid secretion ; pH regulation ; antiport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary pH gradient-dependent sodium transport in highly purified rat parotid basolateral membrane vesicles was studied under voltage-clamped conditions. In the presence of an outwardly directed H+ gradient (pHin=6.0, pHout=8.0)22Na uptake was approximately ten times greater than uptake measured at pH equilibrium (pHin=pHout=6.0). More than 90% of this sodium flux was inhibited by the potassium-sparing diuretic drug amiloride (K 1 =1.6 μm) while the transport inhibitors furosemide (1mm), bumetanide (1mm) SITS (0.5mm) and DIDS (0.1mm) were without effect. This transport activity copurified with the basolateral membrane marker K+-stimulatedp-nitrophenyl phosphatase. In addition22Na uptake into the vesicles could be driven against a concentration gradient by an outwardly directed H+ gradient. pH gradient-dependent sodium flux exhibited a simple Michaelis-Menten-type dependence on sodium concentration cosistent with the existence of a single transport system withK M =8.0mm at 23°C. A component of pH gradient-dependent, amiloride-sensitive sodium flux was also observed in rabbit parotid basolateral membrane vesicles. These results provide strong evidence for the existence of a Na+/H+ antiport in rat and rabbit parotid acinar basolateral membranes and extend earlier less direct studies which suggested that such a transporter was present in salivary acinar cells and might play a significant role in salivary fluid secretion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01925718
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  • 8
    Electronic Resource
    Electronic Resource
    Ionic dependence of bumetanide binding to the rabbit parotid Na/K/Cl cotransporter (1988)
    Springer
    The journal of membrane biology 102 (1988), S. 71-77 
    Details
    ISSN: 1432-1424
    Keywords: loop diuretics ; exocrine gland ; fluid secretion ; parotid ; acinar cell ; ion transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The Na/K/Cl-dependent component of the binding of the loop diuretic bumetanide to basolateral membrane vesicles from the rabbit parotid is studied. A Scatchard analysis indicates that this binding is due to a single high-affinity site withK D =3.2±0.3 μm (n=9) at 100mm sodium, 100mm potassium and 5mm chloride. When KCl-dependent22Na transport and tracer [3H]-bumetanide binding are monitored simultaneously as a function of (unlabeled) bumetanide concentration it is found that theK 0.5 for bumetanide inhibition of both processes are identical indicating that the high-affinity bumetanide binding site studied here is identical with a bumetanide-inhibitory site on the Na/K/Cl cotransport system previously identified in this preparation (R.J. Turner, J.N. George and B.J. Baum,J. Membrane Biol. 94:143–152, 1986). High-affinity bumetanide binding exhibits a hyperbolic dependence on both [Na] and [K] consistent with Na/bumetanide and K/bumetanide binding stoichiometries of 1∶1 andK 0.5 values of approximately 33mm for sodium and 23mm for potassium. In contrast, the dependence on [Cl] is biphasic, with bumetanide binding increasing from 0 to 5mm chloride and decreasing toward baseline levels thereafter. Scatchard analysis of this latter inhibitory effect of chloride indicates a competitive interaction with bumetanide in agreement with earlier indications that bumetanide inhibits Na/K/Cl cotransport at a chloride site. However, studies of the effects of various anions on bumetanide binding and22Na transport show a poor correlation between the specificities of these two processes, suggesting that the inhibitory chloride site is not a chloride transport site.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01875354
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