Splice isoforms of alpha(1a)-adrenoceptor in rabbit

Area of Science:

• Pharmacology
• Molecular Biology
• Genetics

Background:

• The alpha(1a)-adrenergic receptor (AR) plays a crucial role in various physiological processes.
• Understanding the diversity of alpha(1a)-AR isoforms is essential for comprehending receptor function and drug development.

Purpose of the Study:

• To identify and characterize novel splice isoforms of the rabbit alpha(1a)-AR.
• To investigate the pharmacological and functional differences between these isoforms.

Main Methods:

• Isolation of rabbit alpha(1a)-AR splice isoforms from a liver cDNA library.
• Radioligand binding assays using COS-7 cells expressing each isoform.
• Competitive reverse transcription-polymerase chain reaction (RT-PCR) for mRNA distribution analysis.
• Functional assays in CHO cells measuring inositol trisphosphate production, extracellular acidification rate (EAR), and intracellular calcium ([Ca2+]i) concentration.

Main Results:

• Three rabbit alpha(1a)-AR splice isoforms (alpha(1a)-OCU.1-AR, alpha(1a)-OCU.2-AR, and alpha(1a)-OCU.3-AR) were identified with distinct C-terminal sequences.
• All isoforms exhibited high affinity for prazosin and related ligands and low affinity for BMY7378 in binding assays.
• Distinct tissue distribution patterns were observed, with alpha(1a)-OCU.1-AR being most abundant.
• Functional studies revealed similar noradrenaline potency for EAR but varying potency for [Ca2+]i increase, with alpha(1a)-OCU.3-AR showing the highest potency despite lower receptor density.

Conclusions:

• The rabbit alpha(1a)-AR gene produces at least three splice isoforms with unique C-terminal sequences and tissue distribution.
• While binding affinities are similar, functional responses to noradrenaline differ, particularly in [Ca2+]i signaling, suggesting C-terminal variations modulate receptor activity.
• These findings highlight the structural and functional diversity of alpha(1a)-ARs and their potential impact on physiological regulation.