Histamine increases the Ca current in guinea-pig ventricular myocytes

Area of Science:

• Cardiology
• Pharmacology
• Cell Physiology

Background:

• Histamine is a biogenic amine with diverse physiological roles.
• Its effects on cardiac electrophysiology, particularly calcium currents, require further elucidation.

Purpose of the Study:

• To investigate the electrophysiological effects of histamine on guinea-pig ventricular myocytes.
• To determine the specific histamine receptor subtype involved in these cardiac actions.

Main Methods:

• Whole-cell voltage clamp techniques were employed.
• Experiments were conducted on isolated guinea-pig ventricular myocytes.
• Pharmacological agents, cimetidine and mepyramine, were used to probe receptor involvement.

Main Results:

• Histamine significantly prolonged action potential duration.
• Histamine caused an upward shift in the action potential plateau.
• An increase in the inward calcium (Ca) current amplitude was observed.
• A minor increase in outward current was also noted.
• Cimetidine, an H2-receptor antagonist, inhibited histamine's effects.
• Mepyramine, an H1-receptor antagonist, did not affect histamine's actions.

Conclusions:

• Histamine enhances the inward calcium current in ventricular myocytes.
• These effects are likely mediated through the activation of histamine H2-receptors.
• Histamine may play a role in modulating cardiac contractility via calcium current.