Electrical activity-triggered glucagon-like peptide-1 secretion from primary murine L-cells

Non-technical summary Glucagon like peptide 1 (GLP-1) based therapies are now widely used for the treatment of diabetes. The physiological source of the hormone is the intestinal L-cell, and attempts to boost secretion have been hindered by difficulties in distinguishing these cells from their epithelial neighbours and our consequent limited understanding of their physiology. Using recently developed transgenic mice with fluorescently labelled L-cells, we show that these cells are electrically active and use voltage-gated ion channels to couple the presence of nutrients to the secretion of GLP-1. We present the identification and characterisation of the ion channels. This improves our understanding of enteroendocrine physiology and will support therapeutic programmes aiming to target gut hormone secretion.Glucagon like peptide 1 (GLP-1) based therapies are now widely used for the treatment of type 2 diabetes. Developing our understanding of intestinal GLP-1 release may facilitate the development of new therapeutics aimed at targeting the GLP-1 producing L-cells. This study was undertaken to characterise the electrical activity of primary L-cells and the importance of voltage gated sodium and calcium channels for GLP-1 secretion. Primary murine L-cells were identified and purified using transgenic mice expressing a fluorescent protein driven by the proglucagon promoter. Fluorescent L-cells were identified within primary colonic cultures for patch clamp recordings. GLP-1 secretion was measured from primary colonic cultures. L-cells purified by flow cytometry were used to measure gene expression by microarray and quantitative RT-PCR. Electrical activity in L-cells was due to large voltage gated sodium currents, inhibition of which by tetrodotoxin reduced both basal and glutamine-stimulated GLP-1 secretion. Voltage gated calcium channels were predominantly of the L-type, Q-type and T-type, by expression analysis, consistent with the finding that GLP-1 release was blocked both by nifedipine and omega-conotoxin MVIIC. We observed large voltage-dependent potassium currents, but only a small chromanol sensitive current that might be attributable to KCNQ1. GLP-1 release from primary L-cells is linked to electrical activity and activation of L-type and Q-type calcium currents. The concept of an electrically excitable L-cell provides a basis for understanding how GLP-1 release may be modulated by nutrient, hormonal and pharmaceutical stimuli.