Fig. 4. ATP dependence of the rate of exocytosis. Relationship between the maximum rate of exocytosis, measured as the maximum value of the derivative of capacitance traces, and intracellular ATP at the time of patch rupture. A represents mean values obtained using 10 µM Ca²⁺ (n=5-10) and (B) using 300 µM Ca²⁺ (n=3-13) in the pipette. Both sets of values are normalised to their respective value in the control situation. The solid line represents logistic functions fitted to the data. In A K_m=476 µM and a cooperativity factor P=2.6 was obtained. Corresponding values in B were K_m=99 µM and P=7.9.

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