Calcium current in isolated neonatal rat ventricular myocytes

Area of Science:

• Cardiology
• Electrophysiology
• Molecular Biology

Background:

• Neonatal rat ventricular myocytes are a model for studying cardiac ion channels.
• Calcium currents (ICa) play a crucial role in cardiac excitation-contraction coupling.
• Understanding ICa modulation is vital for cardiac drug development.

Purpose of the Study:

• To investigate the biophysical properties of L-type calcium channels in cultured neonatal rat ventricular myocytes.
• To characterize the effects of D600 and BAY K8644 on the steady-state and transient components of ICa.
• To elucidate the mechanisms underlying ICa modulation by specific pharmacological agents.

Main Methods:

• Whole-cell voltage-clamp technique was employed on primary cultured neonatal rat ventricular cells.
• Appropriate voltage protocols were used to isolate and study L-type calcium currents.
• Steady-state activation (d infinity) and inactivation (f infinity) parameters were analyzed.

Main Results:

• The calcium channel antagonist D600 reduced ICa by shifting d infinity and decreasing conductance, without affecting inactivation kinetics.
• The calcium channel modulator BAY K8644 shifted both d infinity and f infinity to more negative potentials, increased inactivation rate, and enhanced conductance, suggesting promotion of 'mode 2' activity.
• A significant steady-state component of ICa ('window current') was observed at plateau potentials.

Conclusions:

• Both D600 and BAY K8644 modulate cardiac calcium currents through distinct effects on steady-state activation and inactivation parameters.
• Pharmacological agents can alter ICa by directly impacting channel gating kinetics (d infinity, f infinity) and potentially channel gating modes.
• These findings provide insights into the complex regulation of cardiac calcium channels and their contribution to cellular electrophysiology.