Inotropic agents modulate gap junctional conductance between cardiac myocytes

Area of Science:

• Cardiovascular Physiology
• Molecular Cardiology
• Cellular Electrophysiology

Background:

• Cardiac gap junction channels are crucial for electrical coupling in the heart.
• Junctional conductance (gj) influences myocardial activation and cardiac rhythm.
• Second messengers like cyclic nucleotides play a role in regulating cardiac function.

Purpose of the Study:

• To investigate the effects of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) on cardiac gap junction conductance.
• To determine the relationship between cyclic nucleotide-mediated changes in gj and inotropic effects.
• To explore the role of intracellular calcium in cAMP-mediated modulation of gj.

Main Methods:

• Measurement of cardiac gap junction conductance (gj) in response to pharmacological agents.
• Utilized agents that elevate intracellular cAMP (e.g., 8-bromo-cAMP, isoproterenol).
• Utilized agents that elevate intracellular cGMP (e.g., 8-bromo-cGMP, carbachol).
• Assessed effects under normal and calcium-overload conditions.

Main Results:

• Elevated intracellular cAMP enhanced cardiac gj.
• Elevated intracellular cGMP depressed cardiac gj.
• These changes occurred with a time course similar to inotropic effects.
• cAMP's effect on gj was independent of simultaneous intracellular calcium changes, but could trigger calcium-dependent uncoupling during overload.

Conclusions:

• Cyclic nucleotide-dependent modulation of cardiac gj significantly contributes to the inotropic effects of these signaling molecules.
• The inotropic effect of cAMP includes a component independent of intracellular calcium.
• Understanding these mechanisms is vital for comprehending cardiac electrophysiology and potential therapeutic interventions.