FIGURE 1.

Reconstitution of depolarization-induced exocytosis in oocytes by expression of exogenous proteins. (A) Diameter and capacitance of plasma membrane and cortical granules in Xenopus oocytes. (B) Effect of depolarization on membrane capacitance in a Xenopus oocyte expressing a voltage-gated Ca²⁺ channel. (Upper trace) Depolarizing voltage command (see Methods), consisting of depolarization from a holding potential of −80 mV to 0 mV for 2 × 500 ms, separated by 100 ms at −80 mV). (C) Continuous monitoring of membrane capacitance showing the effect of depolarization on membrane capacitance (C_m) in an oocyte expressing, Ca²⁺ channel, Lc-type Ca²⁺ channel subunits α₁1.2, β2A, α₂δ; SNAREs: syntaxin 1A, SNAP-25, and synaptotagmin; representative original traces of voltage (upper) current (middle) and C_m (lower). The vertical dashed line indicates the time at which C_m was read for comparison with the baseline C_m before depolarization. (D) Monitoring C_m in oocytes expressing different proteins. Control, uninjected oocytes; other panels, oocytes expressing heterologously synaptic proteins: synaptic proteins, syntaxin 1A, SNAP-25, synaptobrevin, and synaptotagmin, Ca²⁺ channel, Lc-type Ca²⁺ channel subunits α₁1.2, β2A, α₂δ; SNAREs: syntaxin 1A, SNAP-25 and synaptobrevin; synaptotagmin I, sytI; Ca²⁺ channel plus syntaxin 1A, SNAP-25 and syt I. (E) Summary: effect of depolarization on C_m. Groups as in D. ΔC_m, depolarization-induced change of membrane capacitance; bars show mean ± SD (n = 13). (F) Effect of depolarization on membrane current. Depolarization-induced membrane current (InA; mean ± SD, n = 13 each). Data show that the C_m changes (C) cannot be explained by membrane current, but rather reflect bona fide exocytosis.