Volume regulation of nerve terminals

Area of Science:

• Neuroscience
• Cell Biology
• Physiology

Background:

• Presynaptic nerve terminals (synaptosomes) are crucial for neuronal communication.
• Synaptosomes possess regulatory volume increase (RVI) and decrease (RVD) capabilities to maintain cellular homeostasis.
• Understanding synaptosome volume regulation is vital for comprehending neuronal function and dysfunction.

Purpose of the Study:

• To investigate the mechanisms underlying regulatory volume increase (RVI) in synaptosomes.
• To identify the ion transport systems involved in synaptosome volume regulation.
• To elucidate the role of specific ion transporters and inhibitors in RVI.

Main Methods:

• Induction of osmotic challenges (hypotonic and hypertonic) to induce swelling and shrinking.
• Measurement of synaptosome volume changes over time.
• Assessment of RVI rates and steady-state volumes.
• Pharmacological inhibition of ion transport systems using specific drugs (bumetanide, furosemide, ouabain, amiloride).
• Measurement of 86Rb uptake to assess transporter activity.

Main Results:

• Synaptosomes demonstrated rapid RVD (within 2 min) and RVI (initial rate of 0.18%/s).
• RVI was significantly inhibited by the omission of Na+ or K+ ions.
• Loop diuretics bumetanide and furosemide markedly inhibited RVI.
• Bumetanide-sensitive 86Rb uptake was threefold stimulated by hypertonic conditions.
• Ouabain, amiloride, and DIDS did not significantly affect RVI.

Conclusions:

• Synaptosome RVI is primarily mediated by the Na+, K+, Cl- co-transport system.
• Synaptosome shrinking, induced by hypertonic challenges, stimulates this co-transport system.
• The Na+, K+, Cl- co-transporter plays a critical role in maintaining synaptosome volume homeostasis.