[Macrophage activation by synthetic peptides. III. Changes in the membrane potential, Ca2+ content and the regulatory...

Area of Science:

• Immunology
• Cell Biology
• Biophysics

Background:

• Macrophages (MP) play a crucial role in immune responses.
• Cell membrane potential is critical for macrophage function.
• Tuftsin is a known immunomodulatory peptide.

Purpose of the Study:

• To investigate the effects of tuftsin on macrophage membrane potential.
• To elucidate the role of ions (Na+, Ca2+) in tuftsin-induced cellular responses.
• To propose a model for transmembrane ion signaling triggered by tuftsin.

Main Methods:

• Utilized oxonol voltage-sensitive fluorescent dye to measure membrane potential changes.
• Employed Ca(2+)-activated photoprotein obelin to assess intracellular calcium levels.
• Manipulated extracellular Na+ concentration and observed effects on membrane potential.

Main Results:

• Tuftsin induced a biphasic membrane potential change: initial depolarization followed by hyperpolarization.
• Intracellular Ca2+ concentration significantly increased upon tuftsin stimulation, with extracellular Ca2+ as the primary source.
• Tuftsin accelerated the rate of regulatory voltage decrease, similar to calcium ionophores.
• Observed dependence of membrane potential changes on Na+ concentration and disruption by Ca2+ binding.

Conclusions:

• Tuftsin triggers a cascade involving receptor-mediated calcium influx.
• This calcium influx activates non-selective cation channels, allowing Na+ entry.
• The process culminates in Ca(2+)-dependent K+ transport, highlighting a novel signaling pathway.