GLP-1 enhances VDCC activity and [Ca2+]i responses to glucose in HIT-T15 cells overexpressing the wild-type GLP-1 receptor. HIT-T15 cells overexpressing the wild-type GLP-1 receptor were voltage-clamped in the whole-cell configuration under conditions to measure voltage-dependent Ca2+ currents, held at −70 mV and stepped from −60 to 60 mV in 10-mV steps for 250 ms. A: Representative traces for basal control and after sequential cumulative addition of GLP-1 (10−8 mol/l) and nifedipine (10 μmol/l). Current-voltage relationships are shown in B. C: A representative trace of [Ca2+]i in wild-type GLP-1 receptor-transfected HIT-T15 cell measured with Fura 2-AM after sequential cumulative addition of glucose (10 mmol/l), GLP-1, and nifedipine as in A and B.