The endothelin receptor profile in L6 myotubes

Area of Science:

• Molecular Biology
• Cellular Physiology
• Pharmacology

Background:

• Endothelin (ET) peptides are potent vasoactive substances with diverse physiological roles.
• The specific mechanisms of ET action in skeletal muscle cells are not fully elucidated.
• Understanding ET receptor subtypes involved in skeletal muscle is crucial for therapeutic insights.

Purpose of the Study:

• To characterize endothelin (ET) receptors on cultured L6 myotubes.
• To investigate the specific ET receptor subtype mediating ET effects in skeletal muscle cells.
• To elucidate the role of ETA receptors in ET-1-induced calcium signaling in L6 myotubes.

Main Methods:

• Radioligand binding assays using 125I-ET-1 to determine receptor affinity.
• Displacement binding kinetics with unlabeled ET-1, ET-2, and ET-3.
• Pharmacological characterization using selective ETA (JKC-301) and ETB (IRL-1038) receptor antagonists.
• Measurement of cytosolic free calcium (Ca2+) levels in response to ET-1.

Main Results:

• L6 myotubes exhibited high-affinity binding for ET-1 and ET-2 (Kd < 1 nmol/l) and low-affinity binding for ET-3 (Kd > 100 nmol/l), suggesting predominant ETA receptor expression.
• The ETA receptor antagonist JKC-301 effectively blocked ET-1-induced increases in cytosolic free Ca2+.
• The ETB receptor antagonist IRL-1038 did not inhibit the ET-1-evoked calcium response.

Conclusions:

• Cultured L6 myotubes predominantly express functional endothelin ETA receptors.
• The ET-mediated effects on skeletal muscle cells, including calcium mobilization, are primarily mediated through the ETA receptor subtype.
• These findings provide critical insights into the molecular mechanisms of endothelin signaling in skeletal muscle.