Biosensor Cell Array Reveals Temporal GABA Secretion Dynamics from Pancreatic Islets
Pancreatic beta cells have the unique function of synthesizing and secreting high amounts of the inhibitory neurotransmitter {gamma}-aminobutyric acid (GABA). The mechanism of GABA secretion, whether vesicular or channel-mediated, is debated. Our study reveals surprising temporal complexity in the pattern of islet GABA secretion. We used insulin secretion modulators to demonstrate that GABA release is not directly correlated with insulin secretion. VGAT reporter mice also showed that beta cells do not express the requisite vesicular GABA transporter (VGAT) for vesicular GABA release. Instead, GABA is secreted from the cytosol in pulses by the LRRC8A/D isoform of the volume regulatory anion channel (VRAC). We further demonstrate the dynamic coordination of GABA release with calcium influx in beta cells and dependence on beta cell depolarization. These results suggest a model where GABA is released during the peaks of beta cell calcium oscillations to provide feedback which strengthens and reinforces the oscillation waveform.