Sialic acid and the surface charge associated with hyperpolarization-activated, inward rectifying channels

Area of Science:

• Cardiovascular Physiology
• Cellular Electrophysiology
• Molecular Biology

Background:

• Pacemaker cells in the sinoatrial node generate heart rhythm.
• Hyperpolarization-activated, inward rectifying channels (i(f)) are crucial for pacemaker activity.
• The surface charge of these channels influences their function, but its composition is not fully understood.

Purpose of the Study:

• To investigate the role of sialic acid residues (NANA) in the negative surface charge associated with hyperpolarization-activated, inward rectifying channels.
• To test the hypothesis that NANA contributes significantly to this surface charge.

Main Methods:

• Whole-cell patch-clamp technique on cultured rabbit sinoatrial node pacemaker cells.
• Measurement of activation-voltage relationships for i(f) current.
• Application of calcium (Ca2+) and dimethonium to assess surface charge effects.
• Enzymatic treatment with neuraminidase to remove NANA.

Main Results:

• Calcium and dimethonium caused significant shifts in the half-activation potential (V 1/2), confirming the presence of negative surface charges.
• Neuraminidase treatment did not significantly alter V 1/2 or current amplitude, indicating NANA is not the primary source of negative charge.
• Neuraminidase pretreatment did not affect the charge screening effect of dimethonium.

Conclusions:

• Sialic acid residues (NANA) do not constitute the negative surface charge associated with hyperpolarization-activated, inward rectifying channels.
• The negative surface charge likely originates from other components on the myocyte surface.
• Further research is needed to identify the specific molecules responsible for the channel's surface charge.