The Voltage-Gated Ca2+ Channel Is the Ca2+ Sensor Protein of Secretion
| Autor: | Yamit Hagalili, Niv Bachnoff, Daphne Atlas |
|---|---|
| Rok vydání: | 2008 |
| Předmět: |
Calcium Channels
L-Type Chromaffin Cells Transfection Biochemistry Synaptic vesicle Exocytosis Synaptotagmin 1 Electrochemistry Animals Secretion Binding site Binding Sites Voltage-gated ion channel Chemistry Vesicle Depolarization Kinetics Protein Subunits Biophysics Calcium Cattle Mutant Proteins Calcium Channels Protein Binding |
| Zdroj: | Biochemistry. 47:13822-13830 |
| ISSN: | 1520-4995 0006-2960 |
| DOI: | 10.1021/bi801619f |
| Popis: | Neurotransmitter release involves two consecutive Ca(2+)-dependent steps, an initial Ca(2+) binding to the selectivity filter of voltage-gated Ca(2+) channels (VGCC) followed by Ca(2+) binding to synaptic vesicle protein. The unique Ca(2+)-binding site of the VGCC is located within the alpha(1) subunit of the Ca(2+) channel. The structure of the selectivity filter allows for the binding of Ca(2+), Sr(2+), Ba(2+), and La(3+). Despite its cell impermeability, La(3+) supports secretion, which is in contradistinction to the commonly accepted mechanism in which elevation of cytosolic ion concentrations ([Ca(2+)](i)) and binding to synaptotagmin(s) trigger release. Here we show that a Cav1.2-mutated alpha(1)1.2/L775P subunit which does not conduct Ca(2+) currents supports depolarization-evoked release by means of Ca(2+) binding to the pore. Bovine chromaffin cells, which secrete catecholamine almost exclusively via nifedipine-sensitive Cav1.2, were infected with the Semliki Forest Virus, pSFV alpha(1)1.2/L775P. This construct also harbored a second mutation that rendered the channel insensitive to nifedipine. Depolarization of cells infected with alpha(1)1.2/L775P triggered release in the presence of nifedipine. Thus, the initial Ca(2+) binding at the pore of the channel appeared to be sufficient to trigger secretion, indicating that the VGCC could be the primary Ca(2+) sensor protein. The 25% lower efficiency, however, implied that additional ancillary effects of elevated [Ca(2+)](i) were essential for optimizing the overall release process. Our findings suggest that the rearrangement of Ca(2+) ions within the pore of the channel during membrane depolarization triggers secretion prior to Ca(2+) entry. This allows for a tight temporal coupling between the depolarization event and exocytosis of vesicles tethered to the channel. |
| Databáze: | OpenAIRE |
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