Protamine sulfate-induced enzyme secretion from rabbit neutrophils

Area of Science:

• Immunology
• Cell Biology

Background:

• Neutrophils are key immune cells involved in host defense.
• Enzyme secretion is a critical neutrophil function for combating pathogens.

Purpose of the Study:

• To investigate the mechanism by which protamine sulfate induces enzyme secretion from rabbit neutrophils.
• To elucidate the role of calcium and protamine's charge in this process.

Main Methods:

• Rabbit neutrophils were stimulated with protamine sulfate.
• Enzyme secretion and cell lysis were measured.
• The effects of extracellular calcium, other metal ions, and heparin were assessed.
• Protamine conjugated to agarose beads was used to study membrane interactions.

Main Results:

• Protamine sulfate induced significant enzyme secretion, mainly through exocytosis with minimal cytolysis.
• Extracellular calcium was required for optimal exocytosis, but other divalent cations showed partial effects.
• The positive charge of protamine was essential, as indicated by inhibition by heparin and induction by charged agarose beads.
• Sialic acid residues on the neutrophil membrane did not appear to be involved.

Conclusions:

• Protamine sulfate is an effective inducer of neutrophil enzyme secretion via exocytosis.
• The interaction of protamine's positive charges with the neutrophil plasma membrane is the primary trigger.
• This mechanism differs from other neutrophil activators in its kinetics and metabolic requirements.