A 5-HT4-like receptor in human left atrium

Area of Science:

• Cardiology
• Pharmacology
• Molecular Biology

Background:

• Terminal heart failure affects cardiac contractility.
• 5-hydroxytryptamine (5-HT) is a neurotransmitter with potential cardiac effects.
• Understanding 5-HT's role in failing hearts is crucial for therapeutic development.

Purpose of the Study:

• To investigate the effects of 5-hydroxytryptamine (5-HT) on left atrial contractility in patients with terminal heart failure.
• To characterize the specific 5-HT receptor involved and its downstream signaling pathways.
• To determine if this receptor is functional in failing human heart tissue.

Main Methods:

• Isometric tension recordings of human left atrial preparations from heart transplant recipients.
• Pharmacological blockade of beta-adrenoceptors and 5-HT uptake to isolate 5-HT effects.
• Competitive antagonism using a selective 5-HT4 receptor antagonist (ICS 205-930).
• Measurement of cyclic AMP (cAMP) levels and cAMP-dependent protein kinase activity.

Main Results:

• 5-HT significantly increased left atrial contractile force in a concentration-dependent manner (pEC50 = 7.0).
• The effects of 5-HT were competitively antagonized by ICS 205-930 (pKB = 6.8), indicating a 5-HT4-like receptor.
• 5-HT increased intracellular cyclic AMP (cAMP) levels and stimulated cAMP-dependent protein kinase activity.
• The maximal effect of 5-HT on contractility was approximately 25% of that induced by isoprenaline or CaCl2.

Conclusions:

• A functional 5-HT4-like receptor exists in the human left atrium of patients with terminal heart failure.
• This receptor mediates positive inotropic effects and modulates cAMP signaling in failing cardiac tissue.
• The findings suggest a potential therapeutic target for modulating cardiac function in heart failure.