Na(+)-Ca2+ exchange current in latent pacemaker cells isolated from cat right atrium

Area of Science:

• Cardiovascular Physiology
• Cellular Electrophysiology
• Cardiac Pacemaker Function

Background:

• Pacemaker cells in the heart regulate heart rate through complex ionic mechanisms.
• Understanding calcium handling is crucial for comprehending cardiac rhythm and function.

Purpose of the Study:

• To investigate the ionic currents underlying pacemaker activity in cat right atrial cells.
• To characterize a novel inward current component and its relationship with calcium release.

Main Methods:

• Whole-cell patch-clamp recordings using the nystatin-perforated method on isolated cat right atrial pacemaker cells.
• Voltage clamp pulses to elicit and analyze L-type calcium currents (ICa) and a secondary inward current.
• Pharmacological and ionic manipulations (EGTA, ryanodine, lithium substitution) to identify the source of the inward current.

Main Results:

• A secondary inward current, identified as sodium-calcium exchange current (INa-Ca), was observed following L-type calcium current activation.
• INa-Ca is mediated by sarcoplasmic reticulum calcium release and distinct from ICa in voltage dependence and recovery kinetics.
• Isoprenaline enhanced both ICa and INa-Ca, while their voltage-dependent recovery patterns differed.

Conclusions:

• The study identifies a sarcoplasmic reticulum-mediated sodium-calcium exchange current in atrial pacemaker cells.
• This INa-Ca plays a significant role in cardiac electrophysiology and calcium homeostasis.
• Distinct properties of INa-Ca and ICa highlight their unique contributions to pacemaker cell function.