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Ion interaction at the pore of Lc‐type Ca 2+ channel is sufficient to mediate depolarization‐induced exocytosis
Author(s) -
Lerner Immanuel,
Trus Michael,
Cohen Roy,
Yizhar Ofer,
Nussinovitch Itzhak,
Atlas Daphne
Publication year - 2006
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.2006.03709.x
Subject(s) - exocytosis , depolarization , biophysics , chemistry , intracellular , channel blocker , voltage dependent calcium channel , secretion , divalent , calcium , biochemistry , biology , organic chemistry
The coupling of voltage‐gated Ca 2+ channel (VGCC) to exocytotic proteins suggests a regulatory function for the channel in depolarization‐evoked exocytosis. To explore this possibility we have examined catecholamine secretion in PC12 and chromaffin cells. We found that replacing Ca 2+ with La 3+ or other lanthanide ions supported exocytosis in divalent ion‐free solution. Cd 2+ , nifedipine, or verapamil inhibited depolarization‐evoked secretion in La 3+ , indicating specific binding of La 3+ at the pore of L‐type VGCC, probably at the poly‐glutamate (EEEE) locus. Lanthanide efficacy was stringently dependent on ionic radius with La 3+ > Ce 3+ > Pr 3+ , consistent with a size‐selective binding interface of trivalent cations at the channel pore. La 3+ inward currents were not detected and the highly sensitive La 3+ /fura‐2 imaging assay (∼1 p m ) detected no La 3+ entry, cytosolic La 3+ build‐up, or alterations in cytosolic Ca 2 . These results provide strong evidence that occupancy of the pore of the channel by an impermeable cation leads to a conformational change that is transmitted to the exocytotic machinery upstream of intracellular cation build‐up (intracellular Ca 2+ concentration). Our model allows for a tight temporal and spatial coupling between the excitatory stimulation event and vesicle fusion. It challenges the conventional view that intracellular Ca 2+ ion build‐up via VGCC permeation is required to trigger secretion and establishes the VGCC as a plausible Ca 2+ sensor protein in the process of neuroendocrine secretion.