Modulation of the Bursting Properties of Single Mouse Pancreatic β-Cells by Artificial Conductances

• Published in: Biophysical journal Vol. 76; no. 3; pp. 1423 - 1435
• Main Authors: Kinard, T.A., de Vries, G., Sherman, A., Satin, L.S.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.03.1999
• Subjects: Action Potentials - drug effects; Adenosine Triphosphate - metabolism; Animals; Biophysical Phenomena; Biophysics; Calcium Channels - drug effects; Calcium Channels - metabolism; Cell Line; Cricetinae; Electric Conductivity; Glucose - pharmacology; In Vitro Techniques; Insulin - metabolism; Insulin Secretion; Islets of Langerhans - cytology; Islets of Langerhans - drug effects; Islets of Langerhans - physiology; Membrane Potentials; Mice; Patch-Clamp Techniques; Potassium - metabolism
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(99)77303-0

Glucose triggers bursting activity in pancreatic islets, which mediates the Ca 2+ uptake that triggers insulin secretion. Aside from the channel mechanism responsible for bursting, which remains unsettled, it is not clear whether bursting is an endogenous property of individual β-cells or requires an electrically coupled islet. While many workers report stochastic firing or quasibursting in single cells, a few reports describe single-cell bursts much longer (minutes) than those of islets (15–60 s). We studied the behavior of single cells systematically to help resolve this issue. Perforated patch recordings were made from single mouse β-cells or hamster insulinoma tumor cells in current clamp at 30–35°C, using standard K +-rich pipette solution and external solutions containing 11.1 mM glucose. Dynamic clamp was used to apply artificial K ATP and Ca 2+ channel conductances to cells in current clamp to assess the role of Ca 2+ and K ATP channels in single cell firing. The electrical activity we observed in mouse β-cells was heterogeneous, with three basic patterns encountered: 1) repetitive fast spiking; 2) fast spikes superimposed on brief (<5 s) plateaus; or 3) periodic plateaus of longer duration (10–20 s) with small spikes. Pattern 2 was most similar to islet bursting but was significantly faster. Burst plateaus lasting on the order of minutes were only observed when recordings were made from cell clusters. Adding g Ca to cells increased the depolarizing drive of bursting and lengthened the plateaus, whereas adding g KATP hyperpolarized the cells and lengthened the silent phases. Adding g Ca and g KATP together did not cancel out their individual effects but could induce robust bursts that resembled those of islets, and with increased period. These added currents had no slow components, indicating that the mechanisms of physiological bursting are likely to be endogenous to single β-cells. It is unlikely that the fast bursting (class 2) was due to oscillations in g KATP because it persisted in 100 μM tolbutamide. The ability of small exogenous currents to modify β-cell firing patterns supports the hypothesis that single cells contain the necessary mechanisms for bursting but often fail to exhibit this behavior because of heterogeneity of cell parameters.