Figure 2.

A: Membrane potential (top) and holding current (bottom) recorded from the same β-cell under current- and voltage-clamp conditions, respectively. The voltage-clamp recording was obtained at −70 mV. B: Schematic of electrical coupling between β-cells in an intact islet. The green rectangles indicate gap junctions. One β-cell within the islet is voltage-clamped at −70 mV through the recording electrode (pink), and regenerative electrical activity in this cell is therefore prevented. Spontaneous electrical activity in neighboring electrically coupled cells results in an inward current that resembles an inverted burst of action potentials in the voltage-clamped cell. Assuming that electrical activity recorded in the β-cell connected to the patch electrode prior to voltage-clamping approximates that of its neighbors, the total gap-junctional conductance (G_j) can be estimated from the equation G_j = ΔI/ΔV, where ΔV and ΔI represent the current and voltage differences between the plateau current/potential and the most repolarized voltage/least negative current, respectively (as indicated in A).