Ca²⁺ channel activities in pancreatic islet cells. (a) The current density histogram of peak I_Ba in wild-type (filled bars, n = 22) and α_1D^–/– (open bars, n = 27) islets. Total refers to total current density; L represents L-current density; Non-L is the remaining current density. I_Ba was activated by depolarizations from –80 mV to 0 or 10 mV every 10 seconds. (b) Immunostaining of L-type calcium channel subtypes in pancreatic islets. Primary antibodies used are indicated on the left side of the panel. Four independent experiments were performed from three animals per genotype. Bar, 100 μm. (c) Representative current records of I_Ba by whole cell patch clamp in wild-type and α_1D–/– pancreatic islet cells. Depolarizations from –80 mV to levels ranging from –30 to 0 mV in 10-mV increments for 400 microseconds every 10 seconds. (d) Voltage dependence of Ca²⁺ channel currents in wild-type (filled circles, n = 16) and α_1D–/– (open circles, n = 17) β cells. *P < 0.001. The peak I_Ba current was normalized to cell capacitance. Average cell capacitance was 4.35 ± 0.32 pF for α_1D–/– islet cells and 4.16 ± 0.17 pF for wild-type islet cells. (e) Stimulation of insulin release from cultured islets by glucose stimulation. Islets of similar sizes were selected from the α_1D–/– (open bars) and the control mice (α_1D+/+ and α_1D+/–, filled bars). Five to seven animals were used per genotype. The number of measurements (n) for each concentration for each genotype ranged from 4 to 25. *P < 0.05.