Calcium-activated chloride current in rabbit ventricular myocytes

Area of Science:

• Cardiovascular Physiology
• Ion Channel Function
• Cellular Electrophysiology

Background:

• Rabbit ventricular myocytes possess a transient outward current crucial for cardiac function.
• The precise ionic basis of this current has remained incompletely understood, impacting our knowledge of cardiac electrophysiology.

Purpose of the Study:

• To elucidate the ionic mechanism underlying the transient outward current in rabbit ventricular myocytes.
• To characterize the properties and activators/inhibitors of this specific ion current.

Main Methods:

• Whole-cell patch-clamp electrophysiology was employed to record ionic currents.
• Pharmacological agents (cadmium, nisoldipine, ryanodine, caffeine, SITS, DIDS) and ionic manipulations (calcium buffering, potassium and chloride concentration changes) were used to probe current characteristics.

Main Results:

• The current was calcium-dependent, increased by isoproterenol, and blocked by calcium-related agents.
• It was resistant to 4-aminopyridine and tetraethylammonium, and persisted when potassium was replaced by cesium.
• The current was abolished by reducing chloride concentrations and blocked by anion transport inhibitors SITS and DIDS, confirming its chloride nature.
• Voltage-dependence studies indicated outward rectification, with the current appearing positive to calcium current threshold.

Conclusions:

• The 4-aminopyridine-resistant transient outward current in rabbit ventricular myocytes is a calcium-activated chloride current (ICaCl).
• This finding contributes to a deeper understanding of ion transport and electrophysiological regulation in cardiac cells.