Electrophysiological properties of human ß-cell lines EndoC-ßH1 and ßH2 conform with human ß-cells

We have characterized the electrophysiological properties of the human ß-cell lines EndoC-ßH1 and EndoC-ßH2. Both cell lines respond to glucose (6-20mM) with 2- to 3-fold stimulation of insulin secretion, an effect that was mimicked by tolbutamide (0.2mM) and reversed by diazoxide (0.5mM). Glucose-induced insulin release correlated with an elevation of [Ca2+]i, membrane depolarization and increased action potential firing. KATP channel activity at 1mM glucose is low and increasing glucose to 6 or 20mM glucose reduced KATP channel activity to the same extent as the KATP channel blocker tolbutamide (0.2mM). The upstroke of the action potentials in EndoC-ßH1 and –ßH2 cells observed at high glucose principally reflects activation of L- and P/Q-type Ca2+ channels with some small contribution of TTX-sensitive Na+ channels. Action potential repolarization involves activation of voltage-gated Kv2.2 channels and large-conductance Ca2+-activated K+ channels. Exocytosis (measured by measurements of membrane capacitance) was triggered by membrane depolarizations >10ms to membrane potentials above -30mV. Both cell lines were well-granulated (6,000-15,000 granules/cell) and granules consisted of a central insulin core surrounded by a clear halo. We conclude that the EndoC-ßH1 and –ßH2 cells share many features of primary human ß-cells and that they represent a valuable addition to the experimental 'tool box'.