Ryanodine induced block of a cloned human cardiac potassium channel

Area of Science:

• Pharmacology
• Molecular Biology
• Cardiovascular Physiology

Background:

• Cardiac potassium channels, specifically hKvl.5, play a crucial role in regulating heart rhythm.
• Ryanodine is a known modulator of intracellular calcium release channels, but its effects on cardiac potassium channels are less understood.

Purpose of the Study:

• To investigate the effects of ryanodine on the cloned human cardiac potassium channel, hKvl.5.
• To characterize the dose-dependent inhibition of hKvl.5 by ryanodine.

Main Methods:

• Stable expression of the human cardiac potassium channel (hKvl.5) in a mouse L cell line.
• Whole-cell voltage clamp electrophysiology was used to measure channel currents.
• Dose-response relationships and voltage-dependence of ryanodine's effects were analyzed.

Main Results:

• Ryanodine inhibited hKvl.5 peak and late currents in a dose-dependent manner, with an IC50 of 1.2 microM.
• The inhibition of peak current ranged from 11.3% at 10(-7) M to 43.6% at 10(-5) M ryanodine.
• Ryanodine reduced tail current amplitude without altering the time course and showed partial reversibility at concentrations below 10(-6) M.

Conclusions:

• Ryanodine acts as a dose-dependent inhibitor of the hKvl.5 channel.
• The non-voltage-dependent nature of the block suggests a specific binding interaction.
• These findings highlight a potential novel mechanism of ryanodine action on cardiac ion channels.