Effects of 8-bromo-cyclic GMP on slow channel mediated action potentials of 3-days-old embryonic chick ventricle

Area of Science:

• Cardiovascular Physiology
• Molecular Cardiology
• Developmental Biology

Background:

• Cardiac action potentials in early embryonic chick ventricles are primarily driven by slow channels.
• Cyclic nucleotides, cyclic AMP (cAMP) and cyclic GMP (cGMP), are known modulators of ion channel activity.

Purpose of the Study:

• To investigate the role of cGMP in modulating cardiac slow channel activity.
• To determine if cGMP affects slow channel function under basal conditions and when stimulated.

Main Methods:

• Isolated chick embryo ventricles were used to record action potentials.
• The effects of 8-bromo-cyclic GMP (8-Br-cGMP) on action potential parameters were assessed.
• Interactions between 8-Br-cGMP and agents that increase cAMP or directly stimulate slow channels were examined.

Main Results:

• 8-Br-cGMP significantly reduced maximum diastolic potential, maximal upstroke velocity (+Vmax), and overshoot.
• 8-Br-cGMP antagonized the increase in +Vmax and overshoot induced by cAMP-elevating agents (8-bromo-cyclic AMP, isoproterenol, forskolin) and Bay-K-8644.
• These results indicate 8-Br-cGMP inhibits cardiac slow channel activity.

Conclusions:

• cGMP plays a significant inhibitory role in modulating cardiac slow channel activity in the early embryonic chick heart.
• This down-modulation occurs under basal conditions and when slow channel activity is enhanced by cAMP or direct stimulation.
• cGMP is a key regulator of cardiac electrophysiology during early development.