Alternative mechanisms for atriopeptin prohormone processing by isolated perfused rat hearts

Area of Science:

• Cardiovascular Physiology
• Endocrinology
• Molecular Biology

Background:

• The heart releases atriopeptin-28 (AP28), a biologically active peptide, from its storage form, intact prohormone AP126.
• Understanding the processing and release mechanisms of AP28 is crucial for cardiovascular research.

Purpose of the Study:

• To investigate the mechanisms and stimuli involved in the processing of AP126 to AP28 in the isolated perfused rat heart.
• To differentiate the pathways activated by mechanical stretch versus pharmacological stimulation.

Main Methods:

• Utilized an isolated perfused rat heart model.
• Administered mechanical stretch and phenylephrine (an alpha-adrenergic agonist) to stimulate AP release.
• Employed protease inhibitors (aprotinin, p-aminobenzamidine, soybean trypsin inhibitor) and Ca++-free medium to probe processing pathways.
• Analyzed resulting peptides using amino acid sequencing.

Main Results:

• Right atrial stretch and phenylephrine stimulated AP28 release.
• Aprotinin inhibited stretch-induced processing, yielding intact AP126, but not phenylephrine-induced processing.
• Ca++-free medium inhibited stretch-induced processing but not AP release, while suppressing phenylephrine-stimulated release.
• Cleavage in Ca++-free medium occurred at non-specific sites, producing peptides other than AP28.

Conclusions:

• Two distinct AP processing pathways exist in the isolated perfused rat heart, differentially activated by mechanical and pharmacological stimuli.
• The specific enzyme for AP prohormone processing during stretch is Ca++ dependent.
• Nonspecific cleavage pathways do not require Ca++ and are distinct from the specific processing pathway.