Vesicular Ca²⁺-induced secretion promoted by intracellular pH-gradient disruption

The actions of the protonophore CCCP on intracellular Ca²⁺ regulation and exocytosis in chromaffin cells have been examined. Simultaneous fura-2 imaging and amperometry reveal that exposure to CCCP not only perturbs mitochondrial function but that it also alters vesicular storage of Ca²⁺ and catecholamines. By disrupting the pH gradient of the secretory vesicle membrane, the protonophore allows both Ca²⁺ and catecholamine to leak into the cytosol. Unlike the high cytosolic Ca²⁺ concentrations resulting from mitochondrial membrane disruption, Ca²⁺ leakage from secretory vesicles may initiate exocytotic release. In conjunction with previous studies, this work reveals that catalytic and self-sustained vesicular Ca²⁺-induced exocytosis occurs with extended exposure to weak acid or base protonophores.