Developmental changes in the calcium currents in embryonic chick ventricular myocytes.

Area of Science:

• Cardiology
• Developmental Biology
• Electrophysiology

Background:

• Cardiac myocytes possess voltage-gated calcium channels crucial for excitation-contraction coupling.
• Understanding the developmental changes in these channels is vital for comprehending cardiac maturation.

Purpose of the Study:

• To characterize the developmental changes in the components of whole-cell calcium current (ICa) in embryonic chick cardiac myocytes.
• To differentiate and analyze L-type (IL) and T-type (IT) calcium currents during embryonic development.

Main Methods:

• Patch-clamp electrophysiology was used to record whole-cell calcium currents from isolated cardiac myocytes of 7-day and 14-day chick embryos.
• Pharmacological agents (Ni2+, D600, nifedipine) and voltage-dependence analysis were employed to distinguish between L-type and T-type currents.
• Steady-state inactivation and activation curves were analyzed to determine voltage-dependent properties.

Main Results:

• Two distinct calcium currents, L-type (IL) and T-type (IT), were identified in embryonic chick cardiac myocytes.
• Pharmacological sensitivity and voltage-dependence differentiated IL (Ni2+-resistant, D600/nifedipine-sensitive) from IT (Ni2+-sensitive).
• A significant developmental shift was observed, with IT showing a negative shift in activation and inactivation potentials in 14-day embryos compared to 7-day embryos.

Conclusions:

• The primary developmental change in cardiac calcium currents involves a negative voltage-axis shift in the activation and inactivation properties of the T-type current (IT).
• These developmental alterations in ICa components contribute to the maturation of cardiac electrophysiology.
• The identified currents and their developmental changes resemble those found in adult mammalian hearts.