T-type calcium current in latent pacemaker cells isolated from cat right atrium

Area of Science:

• Cardiovascular Physiology
• Electrophysiology
• Cell Biology

Background:

• Pacemaker cells initiate and regulate heart rhythm.
• Calcium currents play a crucial role in cardiac electrical activity and excitation-contraction coupling.
• Understanding ion channel function in different cardiac cell types is vital for comprehending cardiac electrophysiology.

Purpose of the Study:

• To investigate and differentiate T-type (ICa,T) and L-type (ICa,L) calcium currents in latent pacemaker cells from the cat right atrium.
• To determine the contribution of ICa,T to the electrical activity of latent pacemaker cells, particularly during diastolic depolarization.
• To compare the properties and current densities of ICa,T and ICa,L in latent pacemaker cells versus working atrial muscle cells.

Main Methods:

• Whole-cell voltage clamp techniques were employed to record calcium currents.
• Pharmacological agents (cobalt, nifedipine, nickel) were used to distinguish between ICa,T and ICa,L.
• Analysis of voltage dependence of activation and inactivation curves was performed.
• Comparison of current densities between latent pacemaker and working atrial muscle cells.

Main Results:

• Both ICa,T and ICa,L were identified in latent pacemaker cells, with distinct voltage dependencies for activation.
• A significant
• window
• current for ICa,T was observed at voltages relevant to diastolic depolarization.
• ICa,T current density was substantially higher in latent pacemaker cells (3.3 pA/pF) compared to working atrial muscle cells (0.73 pA/pF).
• ICa,L exhibited higher current density (12.5 pA/pF) and different pharmacological sensitivity (nifedipine-sensitive) than ICa,T.
• Nickel ions selectively inhibited ICa,T and prolonged pacemaker cycle length, indicating its functional role.

Conclusions:

• Latent atrial pacemaker cells possess a significant and functionally relevant T-type calcium current (ICa,T).
• ICa,T contributes to the late phase of diastolic depolarization and may play a more substantial role in latent pacemaker activity than previously recognized.
• The distinct properties and higher density of ICa,T in latent pacemakers highlight its importance in determining their unique electrophysiological characteristics compared to working atrial cells.