Fig. 5.

cAMP accelerates exocytosis in hMFBs via increasing P/Q-type Ca²⁺ channel-sensitive release component. (A) Scheme of the pulse. The duration of 0-mV depolarization was varied between 2 and 100 ms, which followed short and strong depolarization (2 ms, 70 mV). The sinusoidal voltage (30 mV, 1,000 Hz) was applied for membrane capacitance (C_m) measurements before and after the depolarization. (B) Ca²⁺ current and C_m were measured without (control, Left) and with cAMP (0.5 mM) in the patch pipette (Right). The depolarization induced the Ca²⁺ currents (Top) and elevated the C_m (Bottom). The examples at the 0-mV depolarization for 2 ms (blue), 50 ms (red), and 100 ms (black) are shown. Note that the increase of the C_m caused by the 2-ms depolarization was prominent with cAMP. Insets are the magnified views of the onsets of Ca²⁺ currents. (C) The same as B, but with data obtained in the presence of ω-agatoxin IVA (Aga, 0.5 μM), P/Q-type Ca²⁺ channel blocker in the bath solution. Note that the capacitance jump (ΔC_m) in response to a 2-ms pulse was inhibited in the presence of cAMP. In B and C, the traces at the 2-ms pulses are the averages of three trials, and the capacitance after the depolarizing pulse was measured at the periods indicated by the dotted lines. Baseline is indicated as a gray dotted line. (D) The ΔC_ms are plotted against the pulse duration. The panels show the blockage of ΔC_ms by Aga under the conditions without (Left) and with cAMP in the patch pipette (Right). The filled and open circles represent the ΔC_ms without and with Aga, and they were fitted by a single (for control) and a double exponential function (for cAMP), whose results are indicated as solid (without Aga) and dashed lines in the graphs (with Aga): 9 to 13 (control) and 10 to 14 (cAMP) without Aga; 8 to 15 (control) and 8 to 13 terminals (cAMP) with Aga.