Exocytotic dynamics of glucagon-like peptide-1 from enteroendocrine L cell line is regulated by actin polymerization

Stimulus-secretion coupling of glucagon-like peptide-1 (GLP-1) from enteroendocrine L cells is important for glucose homeostasis. Although intracellular second messengers including Ca2+ and cAMP, and cellular structures including actin cytoskeleton play roles in induction of exocytosis of GLP-1 granules, little is known about the specific part in the process of exocytosis in which they are involved. Here we explored the role of those molecules by live-cell imaging with mouse L cell line GLUTag cells, and used two stimuli: deoxycholic acid (DCA) and high K+. DCA increased both intracellular Ca2+ and cAMP levels, while high K+ only increased Ca2+. We next monitored a single exocytosis of GLP-1 granules and found that, during the first 10 minutes of stimulation, both stimuli mainly induced the exocytosis from the predocked granules with the plasma membrane before stimulation or granules immediately fused to the plasma membrane without docking. Furthermore, inhibition of actin polymerization suppressed the proportion of exocytosis by the predocked granules. These results suggest that the exocytotic process of GLP-1 granules is determined by interaction with F-actin upon the increase of either Ca2+ or cAMP. Summary statement Exocytotic process of glucagon-like peptide-1 granules from a mouse enteroendocrine L cell line is regulated by actin polymerization immediately after elevation of intracellular Ca2+ or cAMP levels. ### Competing Interest Statement The authors have declared no competing interest. * GLP-1 : glucagon-like peptide-1 GIP : glucose-dependent insulinotropic polypeptide DCA : deoxycholic acid SNARE : soluble NSF attachment protein receptor FI : fluorescence intensity ASBT : apical sodium-dependent bile acid transporter Lat A : latrunculin A RRP : readily releasable pool RP : reserve pool