| 1. |
- Barg, Sebastian, et al.
(author)
-
The stimulatory action of tolbutamide on Ca2+-dependent exocytosis in pancreatic beta cells is mediated by a 65-kDa mdr-like P-glycoprotein
- 1999
-
In: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 96:10, s. 5539-5544
-
Journal article (peer-reviewed)abstract
- Intracellular application of the sulfonylurea tolbutamide during whole-cell patch-clamp recordings stimulated exocytosis >5-fold when applied at a cytoplasmic Ca2+ concentration of 0.17 microM. This effect was not detectable in the complete absence of cytoplasmic Ca2+ and when exocytosis was elicited by guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS). The stimulatory action could be antagonized by the sulfonamide diazoxide, by the Cl--channel blocker 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), by intracellular application of the antibody JSB1 [originally raised against a 170-kDa multidrug resistance (mdr) protein], and by tamoxifen (an inhibitor of the mdr- and volume-regulated Cl- channels). Immunocytochemistry and Western blot analyses revealed that JSB1 recognizes a 65-kDa protein in the secretory granules. This protein exhibited no detectable binding of sulfonylureas and is distinct from the 140-kDa sulfonylurea high-affinity sulfonylurea receptors also present in the granules. We conclude that (i) tolbutamide stimulates Ca2+-dependent exocytosis secondary to its binding to a 140-kDa high-affinity sulfonylurea receptor in the secretory granules; and (ii) a granular 65-kDa mdr-like protein mediates the action. The processes thus initiated culminate in the activation of a granular Cl- conductance. We speculate that the activation of granular Cl- fluxes promotes exocytosis (possibly by providing the energy required for membrane fusion) by inducing water uptake and an increased intragranular hydrostatic pressure.
|
|
| 2. |
- Bokvist, K, et al.
(author)
-
Co-localization of L-type Ca2+ channels and insulin-containing secretory granules and its significance for the initiation of exocytosis in mouse pancreatic B-cells
- 1995
-
In: EMBO Journal. - 1460-2075. ; 14:1, s. 50-57
-
Journal article (peer-reviewed)abstract
- We have monitored L-type Ca2+ channel activity, local cytoplasmic Ca2+ transients, the distribution of insulin-containing secretory granules and exocytosis in individual mouse pancreatic B-cells. Subsequent to the opening of the Ca2+ channels, exocytosis is initiated with a latency < 100 ms. The entry of Ca2+ that precedes exocytosis is unevenly distributed over the cell and is concentrated to the region with the highest density of secretory granules. In this region, the cytoplasmic Ca2+ concentration is 5- to 10-fold higher than in the remainder of the cell reaching concentrations of several micromolar. Single-channel recordings confirm that the L-type Ca2+ channels are clustered in the part of the cell containing the secretory granules. This arrangement, which is obviously reminiscent of the 'active zones' in nerve terminals, can be envisaged as being favourable to the B-cell as it ensures that the Ca2+ transient is maximal and restricted to the part of the cell where it is required to rapidly initiate exocytosis whilst at the same time minimizing the expenditure of metabolic energy to subsequently restore the resting Ca2+ concentration.
|
|
| 3. |
- Eliasson, G, et al.
(author)
-
Bättre kontakt mellan primär-och sjukhusvård. Dansk praksiskonsulentordning i nordiskt perspektiv
- 1998
-
In: Nordisk medicin. - 0029-1420. ; 113:8, s. 272-274
-
Journal article (peer-reviewed)abstract
- A successful model of liaison between the primary and secondary (hospital) levels of health care entails improved co-operation between hospital doctors and general practitioners (GPs). Since its introduction in Denmark in 1991, this approach has been adopted in Sweden and, to a lesser extent, in Norway. Important principles of the model include: 1) both at the primary and secondary level, responsibility for cooperation rests with the physicians themselves; 2) all physicians at both levels are involved; 3) liaison is maintained by selected GPs serving as liaison officers acting in concert under the guidance of a coordinator; 4) liaison officers are responsible for cultivating personal contacts and good relations at hospitals, and promoting interest in and commitment to the system. Evaluation of the model requires both quantitative and qualitative studies. Although few evaluations have been completed, and no definite conclusions can be drawn, the preliminary results of current evaluations in progress in Sweden and Norway are promising, as are the reported experiences of those who use the system. A Nordic ad hoc group has been actively engaged in promoting the quality of primary-secondary health care liaison since 1997.
|
|
| 4. |
- Eliasson, Lena, et al.
(author)
-
PKC-dependent stimulation of exocytosis by sulfonylureas in pancreatic beta cells
- 1996
-
In: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 271:5250, s. 813-815
-
Journal article (peer-reviewed)abstract
- Hypoglycemic sulfonylureas represent a group of clinically useful antidiabetic compounds that stimulate insulin secretion from pancreatic beta cells. The molecular mechanisms involved are not fully understood but are believed to involve inhibition of potassium channels sensitive to adenosine triphosphate (KATP channels) in the beta cell membrane, causing membrane depolarization, calcium influx, and activation of the secretory machinery. In addition to these effects, sulfonylureas also promoted exocytosis by direct interaction with the secretory machinery not involving closure of the plasma membrane KATP channels. This effect was dependent on protein kinase C (PKC) and was observed at therapeutic concentrations of sulfonylureas, which suggests that it contributes to their hypoglycemic action in diabetics.
|
|
| 5. |
- Gromada, Jesper, et al.
(author)
-
CaM kinase II-dependent mobilization of secretory granules underlies acetylcholine-induced stimulation of exocytosis in mouse pancreatic B-cells
- 1999
-
In: Journal of Physiology. - 1469-7793. ; 518:3, s. 745-759
-
Journal article (peer-reviewed)abstract
- 1. Measurements of cell capacitance were used to investigate the mechanisms by which acetylcholine (ACh) stimulates Ca2+-induced exocytosis in single insulin-secreting mouse pancreatic B-cells. 2. ACh (250 microM) increased exocytotic responses elicited by voltage-clamp depolarizations 2.3-fold. This effect was mediated by activation of muscarinic receptors and dependent on elevation of the cytoplasmic Ca2+ concentration ([Ca2+]i) attributable to mobilization of Ca2+ from intracellular stores. The latter action involved interference with the buffering of [Ca2+]i and the time constant (tau) for the recovery of [Ca2+]i following a voltage-clamp depolarization increased 5-fold. As a result, Ca2+ was present at concentrations sufficient to promote the replenishment of the readily releasable pool of granules (RRP; > 0.2 microM) for much longer periods in the presence than in the absence of the agonist. 3. The effect of Ca2+ on exocytosis was mediated by activation of CaM kinase II, but not protein kinase C, and involved both an increased size of the RRP from 40 to 140 granules and a decrease in tau for the refilling of the RRP from 31 to 19 s. 4. Collectively, the effects of ACh on the RRP and tau result in a > 10-fold stimulation of the rate at which granules are supplied for release.
|
|
| 6. |
- Göpel, Sven, et al.
(author)
-
Activation of Ca(2+)-dependent K(+) channels contributes to rhythmic firing of action potentials in mouse pancreatic beta cells
- 1999
-
In: Journal of General Physiology. - 0022-1295 .- 1540-7748. ; 114:6, s. 759-770
-
Journal article (peer-reviewed)abstract
- We have applied the perforated patch whole-cell technique to beta cells within intact pancreatic islets to identify the current underlying the glucose-induced rhythmic firing of action potentials. Trains of depolarizations (to simulate glucose-induced electrical activity) resulted in the gradual (time constant: 2.3 s) development of a small (<0.8 nS) K(+) conductance. The current was dependent on Ca(2+) influx but unaffected by apamin and charybdotoxin, two blockers of Ca(2+)-activated K(+) channels, and was insensitive to tolbutamide (a blocker of ATP-regulated K(+) channels) but partially (>60%) blocked by high (10-20 mM) concentrations of tetraethylammonium. Upon cessation of electrical stimulation, the current deactivated exponentially with a time constant of 6.5 s. This is similar to the interval between two successive bursts of action potentials. We propose that this Ca(2+)-activated K(+) current plays an important role in the generation of oscillatory electrical activity in the beta cell.
|
|
| 7. |
- Kjerrulf, Martin, et al.
(author)
-
Interferon-gamma receptor-deficient mice exhibit impaired gut mucosal immune responses but intact oral tolerance.
- 1997
-
In: Immunology. - 0019-2805. ; 92:1, s. 60-8
-
Journal article (peer-reviewed)abstract
- Interferon-gamma (IFN-gamma) receptor knock-out (IFN-gamma R -/-) mice were used to analyse the role of IFN-gamma in mucosal immune responses following oral immunization. We found that the IFN-gamma R -/- mice demonstrated 50% reduced spot-forming cell (SFC) responses in the gut lamina propria and spleen after oral immunization with keyhold limpet haemocyanin (KLH) plus cholera toxin (CT) adjuvant. The IFN-gamma R -/- mice exhibited 10-fold reduced total serum KLH-specific antibody levels compared with wild-type mice after oral immunization, while after intravenous immunization, no such difference was seen, suggesting a selective impairment of mucosal immune responses. Moreover, oral immunizations resulted in impaired interleukin-4 (IL-4), IL-10 and IFN-gamma production by spleen T cells from IFN-gamma R -/- mice, indicating that no reciprocal up-regulation of Th2-activities had occurred despite the lack of IFN-gamma R function. No reduction in Th1 or Th2 cytokines was observed following systemic immunizations. Despite potentially strong modulating effects of IFN-gamma on epithelial cell IgA transcytosis and electrolyte barrier functions, CT-immunized IFN-gamma R -/- mice demonstrated unaltered protection against CT in ligated intestinal loops together with normal anti-CT IgA and total IgA levels in gut lavage. Oral feeding with KLH followed by parenteral immunization resulted in strongly suppressed SFC numbers and reduced cell-mediated immunity in both wild-type and IFN-gamma R -/- mice. CT-adjuvant abrogated induction of oral tolerance in both IFN-gamma R -/- and wild-type mice. Collectively, our data argue that the two major response patterns induced by oral administration of protein antigen, i.e. active IgA immunity and oral tolerance, are differently regulated. Thus, IFN-gamma R -/- mice have impaired mucosal immune responses while induction of oral tolerance appears to be unaffected by the lack of IFN-gamma functions.
|
|
| 8. |
|
|
