Fig. 4.

Role of transient receptor potential channels in peptone-stimulated GLP-1 secretion.

(a) A representative trace showing intracellular calcium changes in a primary duodenal L-cell before, during and after the application of meat peptones (pep, 5 mg/ml) and co-application of lanthanum chloride (LaCl₃, 50 μM). (b) Mean calcium changes in L-cells following the addition of peptone in the presence (n = 9) and absence (n = 9) of lanthanum chloride and KCl (n = 7). Co-application of lanthanum chloride significantly inhibited peptone- stimulated rise in intracellular calcium. Data represent the mean ± SEM. **p < 0.01, ***p < 0.001 compared with baseline and between conditions by one- and two-sample Student’s t test. (c) Representative trace showing intracellular calcium changes in primary duodenal L-cells before, during and after the application of KCl (30 mM) and co-application of lanthanum chloride (LaCl₃, 50 μM). (d) Representative trace showing intracellular calcium changes in primary duodenal L-cells before, during and after the application of KCl (30 mM) and co-application of cobalt chloride (CoCl₂, 5 mM). (e) Mean calcium changes in L-cells following the addition of KCl in the absence (n = 17) and presence of lanthanum chloride (n = 16) and cobalt chloride (n = 6). Co-application of cobalt chloride significantly inhibited KCl- stimulated rise in intracellular calcium. Data represent the mean ± SEM. **p < 0.01, ***p < 0.001 compared with baseline and ^##p < 0.01 compared with KCl alone by one- and two-sample Student’s t test. (f) GLP-1 secretion from murine small intestine cultures incubated for 2 h in the presence of peptones (n = 19) and TRP channel inhibitors, lanthanum chloride (LaCl₃, 50 μM, n = 19). GLP-1 secretion in each well is expressed relative to the basal secretion (control) measured in parallel on the same. Data represent the mean ± SEM. **p < 0.01, ***p < 0.01 compared with their respective controls by one-way ANOVA with post hoc Bonferroni analysis.