Synaptic vesicle Ca2+/H+ antiport: dependence on the proton electrochemical gradient

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Synaptic vesicles store neurotransmitters and regulate intracellular calcium.
• Calcium homeostasis is crucial for neuronal function.
• The mechanisms of calcium transport in synaptic vesicles are not fully understood.

Purpose of the Study:

• To investigate the mechanism of Ca2+ accumulation in sheep brain synaptic vesicles.
• To determine the role of the proton motive force (PMF) in Ca2+ transport.
• To elucidate the dependence of Ca2+/H+ antiport on the electrochemical gradient components.

Main Methods:

• Isolation of synaptic vesicles from sheep brain cortex.
• Measurement of Ca2+ uptake and H+ release.
• Manipulation of the proton gradient (DeltapH) and membrane potential (Deltaphi).
• Use of specific H+-pump inhibitors (bafilomycin A1, ergocryptine, folimycin, DCCD).

Main Results:

• Synaptic vesicles accumulate Ca2+ via secondary active transport linked to H+-pump activity.
• Ca2+ uptake is primarily driven by the chemical gradient (DeltapH), with a smaller contribution from the electrical gradient (Deltaphi).
• Ca2+/H+ antiport activity is dependent on the magnitude of DeltapH, with optimal activity observed at specific Ca2+ concentrations.

Conclusions:

• Synaptic vesicle Ca2+/H+ antiport is indirectly linked to ATP hydrolysis.
• The Ca2+ accumulation mechanism is essentially dependent on the DeltapH component of the PMF generated by H+-pumps.
• Understanding this transport mechanism is vital for synaptic function and calcium signaling in neurons.