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Cell-Specific Ca2+ Response in Pancreatic ß-cells
Umeå University, Faculty of Medicine, Integrative Medical Biology, Histology and Cell Biology.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Pancreatic ß-cells are heterogeneous in their secretory responsiveness, glucose sensitivity and metabolic rate. A diminished and delayed first-phase insulin release is an early sign of failing ß-cells in diabetes. Mechanisms controlling functional characteristics, such as lag time for insulin release or magnitude of the response in each individual cell are unknown. To find out whether the heterogeneity represents a random phenomenon in ß-cell or is a manifestation of reproducible characteristics, we compared parameters of Ca2+ response in Fura-2 labelled ob/ob mouse ß-cells during two consecutive stimulations with glucose. Lag times, as well as peak heights and nadirs of initial lowering showed a strong correlation between the first and second stimulation. Thus, timing and magnitude of the early Ca2+ response were specific for each cell. ß-Cells from lean mice, diabetic db/db mice and rats also showed cell-specific responses characteristics. This indicates that a cell-specific Ca2+ response to glucose is common in rodent ß-cells, both normal and diabetic. Another question was whether aggregated ß-cells show cell-specific responses. Using the same protocol as for dispersed ß-cells, we analysed Ca2+ responses in clusters of different size and in intact islets from ob/ob and lean mice. Correlations were found between the first and second stimulation for timing and magnitude of [Ca2+]i rise, and for the initial lowering.

Next, we tested if the ß-cell response is cell-specific, when induced at different steps of the stimulus-secretion coupling. The glycolytic intermediate glyceraldehyde, the mitochondrial substrate KIC, the KATP-channel blocker tolbutamide and arginine were used as tools. [Ca2+]i changes were studied in dispersed ß-cells from lean, ob/ob and db/db mice. NADH responses to glucose and KIC were analyzed as a measure of metabolic flux. The correlation between Ca2+ and insulin response from individual ß-cells was tested using Fluo-3 and Fluozin-3.

Both timing and magnitude of calcium responses were cell-specific in lean mouse ß-cells with all tested secretagogues. ß-Cells from ob/ob and db/db mice showed cell-specific timing of Ca2+ responses to glyceraldehyde but not to KIC, tolbutamide or arginine. However, ob/ob mouse ß-cells within intact islets showed cell-specific timing of tolbutamide-induced response. NADH responses to glucose were cell-specific in all three mouse models, but the timing of NADH responses to KIC was cell-specific only in lean mice. Thus, a cell-specific response can be induced in normal ß-cells at several steps of stimulus-secretion coupling for nutrient-stimulated insulin release. Cell-specific properties of ß-cell ion channels and the mitochondrial metabolism are affected in db/db and ob/ob mice.

The relation between mitochondrial mass and parameters of Ca2+ responses were investigated in Mitotracker Red and Fluo-3 labelled ß-cells using confocal microscopy. Data show that ß-cell mitochondrial state may play an important role in determining the timing of [Ca2+]i changes.

In summary, the early Ca2+ response pattern in ß-cells, including the lag time, the nadir of initial lowering and the height of the first peak response is cell-specific. Isolated and functionally coupled ß-cells show cell-specific timing of Ca2+ responses when stimulated with metabolic and non-metabolic agents. This may be a robust mechanism of importance for the adequate function of ß-cells and a basis for the pacemaker function of some cells. A disturbed cell specificity of the mitochondrial metabolism and ion channel function appears to be a marker of ß-cell dysfunction in hyperglycemia and diabetes and may explain the delayed insulin release in ß-cells from diabetic subjects.

Place, publisher, year, edition, pages
Umeå: Integrativ medicinsk biologi , 2005. , 46 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1000
Keyword [en]
heterogeneity; individual ß-cells; islets of Langerhans; cytoplasmic calcium; repetitive glucose stimulation; lag-time; cell-specific; glyceraldehyde; ketoisocaproic acid; tolbutamide; mitochondrial metabolism
National Category
Cell and Molecular Biology
Identifiers
URN: urn:nbn:se:umu:diva-661ISBN: 91-726-4000-6 (print)OAI: oai:DiVA.org:umu-661DiVA: diva2:144158
Public defence
2006-01-13, BiA201, Histologi, Umeå Universitet, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2005-12-21 Created: 2005-12-21 Last updated: 2009-11-13Bibliographically approved
List of papers
1. Isolated mouse pancreatic β-cells show cell-specific temporal response pattern
Open this publication in new window or tab >>Isolated mouse pancreatic β-cells show cell-specific temporal response pattern
2002 (English)In: American Journal of Physiology - Cell Physiology, ISSN 0363-6143, E-ISSN 1522-1563, Vol. 282, no 6, C1199-C1204 p.Article in journal (Refereed) Published
Abstract [en]

The length of the silent lag time before elevation of the cytosolic free Ca2+ concentration ([Ca2+]i) differs between individual pancreatic beta-cells. One important question is whether these differences reflect a random phenomenon or whether the length of lag time is inherent in the individual beta-cell. We compared the lag times, initial dips, and initial peak heights for [Ca2+]i from two consecutive glucose stimulations (with either 10 or 20 mM glucose) in individual ob/ob mouse beta-cells with the fura 2 technique in a microfluorimetric system. There was a strong correlation between the lengths of the lag times in each beta-cell (10 mM glucose: r = 0.94, P < 0.001; 20 mM glucose: r = 0.96, P < 0.001) as well as between the initial dips in [Ca2+]i (10 mM glucose: r = 0.93, P < 0.001; 20 mM glucose: r = 0.79, P < 0.001) and between the initial peak heights (10 mM glucose: r = 0.51, P < 0.01; 20 mM glucose: r = 0.77, P < 0.001). These data provide evidence that the response pattern, including both the length of the lag time and the dynamics of the subsequent [Ca2+]i, is specific for the individual beta-cell.

Place, publisher, year, edition, pages
?, 2002
Identifiers
urn:nbn:se:umu:diva-4883 (URN)10.1152/ajpcell.00009.2001 (DOI)11997233 (PubMedID)
Available from: 2005-12-21 Created: 2005-12-21 Last updated: 2010-06-24Bibliographically approved
2. Cell-specific Ca2+ responses in glucose-stimulated single and aggregated ß-cells
Open this publication in new window or tab >>Cell-specific Ca2+ responses in glucose-stimulated single and aggregated ß-cells
2003 (English)In: Cell Calcium, ISSN 0143-4160, E-ISSN 1532-1991, Vol. 34, no 2, 121-129 p.Article in journal (Refereed) Published
Abstract [en]

A rise in the cytoplasmic calcium concentration ([Ca(2+)](i)) is a key event for insulin exocytosis. We have recently found that the 'early [Ca(2+)](i) response' in single ob/ob mouse beta-cells is reproduced during consecutive glucose stimulations. It, therefore, appears that the response pattern is a characteristic of the individual beta-cell. We have now investigated if a cell-specific [Ca(2+)](i) response is a general phenomenon in rodent beta-cells, and if it can be observed when cells are functionally coupled. With the use of the fura-2 technique, we have studied the 'early [Ca(2+)](i) response' in single dispersed beta-cells, in beta-cell clusters of different size and in intact islets from the ob/ob mouse during repeated glucose stimulation (20mM). beta-Cells from lean mouse and rat, and intact islets from lean mouse were also investigated. Significant correlations between the first and second stimulation were found for the parameters lag-time for Ca(2+) rise (calculated as the time from start of stimulation of the cell until the first value above an extrapolated baseline), nadir of initial lowering (difference between the baseline and lowest [Ca(2+)](i) value), and peak height (difference between baseline and the highest [Ca(2+)](i) value of the first calcium peak) in single dispersed beta-cells, in 'single beta-cell within a small cluster', in clusters of medium and large size, and in single dispersed beta-cells from lean mouse and rat. The lag-times for Ca(2+) rise and peak heights were correlated within the pairs of stimulation also in intact ob/ob islets. In summary, despite a large heterogeneity of the 'early [Ca(2+)](i) response' among individual cells, the lag-time for [Ca(2+)](i) rise, the nadir of initial lowering and the height of the first peak response can be identified as cell-specific markers in beta-cells.

Place, publisher, year, edition, pages
Elsevier ScienceDirect, 2003
Keyword
Islets of Langerhans, Lag-time, Heterogeneity, Calcium, Cell specific
Identifiers
urn:nbn:se:umu:diva-4884 (URN)10.1016/S0143-4160(03)00027-7 (DOI)12810054 (PubMedID)
Available from: 2005-12-21 Created: 2005-12-21 Last updated: 2010-06-24Bibliographically approved
3. Pancreatic beta cells from db/db mice show cell-specific [Ca2+]i and NADH responses to glucose but not to alpha-ketoisocaproic acid.
Open this publication in new window or tab >>Pancreatic beta cells from db/db mice show cell-specific [Ca2+]i and NADH responses to glucose but not to alpha-ketoisocaproic acid.
2005 (English)In: Pancreas, ISSN 0885-3177, E-ISSN 1536-4828, Vol. 31, no 3, 242-250 p.Article in journal (Refereed) Published
Abstract [en]

OBJECTIVE: We recently showed that timing and magnitude of the glucose-induced cytoplasmic calcium [Ca2+]i response are reproducible and specific for the individual beta cell. We now wanted to identify which step(s) of stimulus-secretion coupling determine the cell specificity of the [Ca2+]i response and whether cell specificity is lost in beta-cells from diabetic animals. Besides glucose, we studied the effects of glyceraldehyde, a glycolytic intermediate, and alpha-ketoisocaproic acid (KIC), a mitochondrial substrate. METHODS: Early [Ca2+]i changes were studied stimulations in fura-2-labeled dispersed beta cells from lean, ob/ob, and db/db mice. Lag time and peak height were compared during 2 consecutive stimulations with the same stimulator. Nicotinamide adenine dinucleotide (NADH) responses to glucose and KIC were studied as a measure of metabolic flux. RESULTS: Both glyceraldehyde and KIC induced cell-specific temporal responses in lean mouse beta cells with a correlation between lag times for [Ca2+]i rise during the first and second stimulation. Beta cells from ob/ob and db/db mice showed cell-specific temporal [Ca2+]i responses to glucose and glyceraldehyde but not to KIC. Glucose induced cell-specific NADH responses in all 3 models, but KIC did so only in lean mouse [beta] cells. CONCLUSIONS: A cell-specific response may be induced at several steps of beta-cell stimulus-secretion coupling. Mitochondrial metabolism generates a cell-specific response in normal beta cells but not in db/db and ob/ob mouse beta cells.

Keyword
Animals, Body Weight, Calcium/*metabolism, Diabetes Mellitus; Type 2/*metabolism, Glucose/*pharmacology, Glycolysis/physiology, Insulin-Secreting Cells/cytology/drug effects/*metabolism, Keto Acids/*pharmacology, Mice, Mice; Obese, Mitochondria/metabolism, NAD/*metabolism, Signal Transduction/drug effects/physiology
Identifiers
urn:nbn:se:umu:diva-12233 (URN)16163056 (PubMedID)
Available from: 2008-01-11 Created: 2008-01-11 Last updated: 2010-06-24Bibliographically approved
4. Cell specificity of Ca2+ response to tolbutamide is impaired in ß-cells from hyperglycemic mice
Open this publication in new window or tab >>Cell specificity of Ca2+ response to tolbutamide is impaired in ß-cells from hyperglycemic mice
2006 (English)In: Journal of Endocrinology, ISSN 0022-0795, E-ISSN 0022-0795, Vol. 190, no 2, 461-470 p.Article in journal (Refereed) Published
Keyword
diabetes mellitus, pancreatic islets, insulin secretagogues, intact islets, amino-acids, delta-cells, b-cells, glucose, secretion, single
National Category
Endocrinology and Diabetes
Identifiers
urn:nbn:se:umu:diva-4886 (URN)10.1677/joe.1.06794 (DOI)
Available from: 2005-12-21 Created: 2005-12-21 Last updated: 2014-03-11Bibliographically approved
5. Timing of Ca2+ response in pancreatic ß-cells is related to mitochondrial mass
Open this publication in new window or tab >>Timing of Ca2+ response in pancreatic ß-cells is related to mitochondrial mass
(English)Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-4887 (URN)
Available from: 2005-12-21 Created: 2005-12-21 Last updated: 2010-06-24Bibliographically approved

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