Streaming potentials reveal a short ryanodine-sensitive selectivity filter in cardiac Ca2+ release channel

Area of Science:

• Biophysics
• Ion Channel Physiology
• Membrane Transport

Background:

• Cardiac sarcoplasmic reticulum Ca2+ release channels (ryanodine receptors) are crucial for muscle contraction.
• Understanding ion and water permeation through these channels is vital for cellular function.

Purpose of the Study:

• To investigate the physical dimensions of the cardiac Ca2+ release channel's permeation pathway.
• To determine the length of the selectivity filter and the effect of ryanodine modification.

Main Methods:

• Reconstitution of single cardiac Ca2+ release channels into planar lipid bilayers.
• Measurement of streaming potentials in osmotically asymmetric solutions.
• Use of valinomycin to correct for concentration polarization and ion activity changes.

Main Results:

• Streaming potentials indicated a short selectivity filter, accommodating approximately 3 water molecules.
• Ryanodine modification abolished measurable streaming potentials.
• Ryanodine increased Tris+ permeability and decreased divalent cation selectivity, suggesting channel widening.

Conclusions:

• The selectivity filter of the cardiac Ca2+ release channel is short.
• Ryanodine binding likely widens the channel's narrowest region, altering its ion permeation properties.