Voltage-dependent intracellular pH in Helix aspersa neurones

Area of Science:

• Neuroscience
• Cell Physiology
• Biophysics

Background:

• Intracellular pH (pHi) regulation is crucial for neuronal function.
• Previous studies indicated that pHi regulation in Helix aspersa nerve cells is sensitive to 4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonic acid (SITS) at resting potentials.

Purpose of the Study:

• To investigate the effects of membrane potential on intracellular pH (pHi) in large nerve cells of Helix aspersa.
• To characterize the ion transport pathway responsible for pHi changes during depolarization.

Main Methods:

• Measurement of intracellular pH (pHi) using pH-sensitive micro-electrodes in voltage-clamped Helix aspersa nerve cells.
• Application of various ionic solutions, including calcium-free saline, and pharmacological agents to probe ion transport mechanisms.
• Testing the effects of different holding potentials on pHi.

Main Results:

• Depolarization from resting potential (-50 mV) to -10 mV caused a decrease in pHi, which was reduced in calcium-free conditions.
• At positive holding potentials, pHi increased, dependent on the electrochemical gradient for H+.
• The depolarization-induced H+ permeability was insensitive to SITS but could be rapidly recovered even in its presence.
• This H+ pathway was insensitive to metabolic inhibitors (CCmP, DCCD, oligomycin) and blocked by heavy metal ions (Zn2+, La3+, Cu2+, Cd2+, Co2+).

Conclusions:

• Depolarization induces a calcium-independent H+ efflux pathway in Helix aspersa nerve cells.
• This pathway is distinct from the SITS-sensitive pHi regulatory mechanism at resting potentials.
• The H+ pathway is likely mediated by a channel permeable to protons, sensitive to specific divalent cations.