Protamine reversibly decreases paracellular cation permeability in Necturus gallbladder.

Area of Science:

• Physiology
• Cell Biology
• Biochemistry

Background:

• Tight junctions regulate paracellular permeability in epithelial tissues.
• Polycationic proteins like protamine can interact with cell membranes and influence ion transport.

Purpose of the Study:

• To investigate the effect of protamine on the electrical resistance and ion permeability of the Necturus gallbladder epithelium.
• To elucidate the mechanism by which protamine alters tight junction function.

Main Methods:

• Transepithelial AC-impedance technique was used to measure electrical resistance in Necturus gallbladder.
• Protamine sulfate/hydrochloride was applied to the mucosal bath, and effects on resistance, voltage, and ion conductance were monitored.
• Reversal of protamine's effects was tested using mucosal heparin and serosal ouabain.

Main Results:

• Protamine significantly increased transepithelial resistance by 89% and altered transepithelial voltage.
• The effects were concentration-dependent, with maximal response at 10-20 microM.
• Protamine reversibly decreased K+ and Na+ conductance by a factor of 3 but not Cl- conductance.
• Net water transport increased by 60% with protamine, and effects were reversible by heparin.

Conclusions:

• Protamine reversibly decreases the conductance of the cation-selective pathway through the tight junction.
• Protamine may exert its effect by binding to the apical membrane, inducing intracellular events that alter tight junction structure.
• This suggests a novel mechanism for regulating paracellular permeability by polycationic proteins.