Slow inward tail currents in rabbit cardiac cells

Area of Science:

• Cardiology
• Electrophysiology
• Molecular Biology

Background:

• Slow inward tail currents play a role in cardiac action potentials.
• The precise mechanisms and modulators of these currents are not fully understood.

Purpose of the Study:

• To investigate the generation and modulation of slow inward tail currents in rabbit cardiac myocytes.
• To test hypotheses regarding the involvement of the sodium-calcium exchanger and intracellular calcium dynamics.

Main Methods:

• Whole-cell voltage-clamp technique on enzymatically dispersed rabbit ventricular and atrial myocytes.
• Application of various stimulation protocols, Tyrode solutions, and pharmacological agents.
• Manipulation of extracellular ion concentrations (Ca2+, K+) and temperature.

Main Results:

• Slow inward tail currents are activated by depolarizing pulses and their decay rate depends on pulse duration.
• Inhibition of the Na(+)-K+ pump or reduced extracellular K+ increased tail current amplitude, suggesting a role for intracellular calcium.
• Barium ions (Ba2+) inhibited the currents, while strontium ions (Sr2+) did not, supporting the involvement of the Na(+)-Ca2+ exchanger.
• Increased extracellular K+ inhibited the slow inward tail currents.

Conclusions:

• The slow inward tail current is primarily generated by an electrogenic Na(+)-Ca2+ exchanger.
• Intracellular calcium release from the sarcoplasmic reticulum modulates the Na(+)-Ca2+ exchanger activity.
• Calcium uptake by the sarcoplasmic reticulum influences the time course of the tail current.