Extracellular Ba(2+) blocks the cardiac transient outward K(+) current

Area of Science:

• Cardiovascular Physiology
• Ion Channel Electrophysiology
• Pharmacology

Background:

• Barium ions (Ba2+) are commonly used in patch-clamp studies.
• Ba2+ is known to block various potassium (K+) channels and pass calcium (Ca2+) channels.
• The specific effect of Ba2+ on cardiac transient outward K+ current (I(to)) requires detailed investigation.

Purpose of the Study:

• To investigate the potential of Ba2+ to block the cardiac transient outward K+ current (I(to)).
• To quantify the potency and characteristics of Ba2+ blockade on I(to).

Main Methods:

• Whole-cell patch-clamp recordings were performed on canine ventricular and atrial myocytes.
• Extracellular application of Ba2+ was used to assess its effects on ion currents.
• Dose-response relationships and voltage-dependence were analyzed.

Main Results:

• Extracellular Ba2+ demonstrated potent inhibition of I(to) with an IC50 of approximately 40 microM.
• Ba2+ blockade of I(to) was voltage-independent and did not alter inactivation kinetics.
• Ba2+ was approximately 10 times more potent than 4-aminopyridine in blocking I(to).
• Ba2+ blockade of inward rectifier K+ current was voltage-dependent, with a significantly lower IC50 at hyperpolarizing potentials.

Conclusions:

• Barium ions (Ba2+) are a potent blocker of the cardiac transient outward K+ current (I(to)).
• Ba2+ can be considered a valuable pharmacological tool for studying I(to) in cardiac electrophysiology.
• The differential effects of Ba2+ on various K+ currents highlight its specific utility in channel research.