High affinity binding of ramiprilat on isolated human glomeruli

Area of Science:

• Nephrology
• Biochemistry
• Pharmacology

Background:

• Angiotensin-converting enzyme (ACE) plays a crucial role in the renin-angiotensin system.
• The presence and localization of ACE within human glomeruli are of significant interest for understanding renal physiology and pathology.

Purpose of the Study:

• To provide evidence for the presence of ACE on isolated human glomeruli.
• To characterize the binding kinetics and specificity of a potent ACE inhibitor, ramiprilat, to human glomeruli.

Main Methods:

• Utilized tritium-labeled ramiprilat (3H-ramiprilat) for binding assays on isolated human glomeruli.
• Investigated binding kinetics (KD, Bmax), temperature and time dependence, and specificity through competition assays with enalaprilat and antibodies against ACE.
• Assessed the role of zinc ions using EGTA and determined optimal pH for binding.

Main Results:

• Demonstrated specific binding of 3H-ramiprilat to isolated human glomeruli (KD = 3.8 nmol/l, Bmax = 853 fmol/mg protein), with specific binding exceeding 90% of total binding.
• Observed rapid dissociation of 3H-ramiprilat upon dilution or addition of unlabeled inhibitor.
• Showed inhibition of binding by enalaprilat, anti-ACE antibodies, and EGTA (chelator of zinc ions), with reversal by Zn2+ and Ca2+.
• Identified optimal binding at pH 8.

Conclusions:

• The specific binding of 3H-ramiprilat to isolated human glomeruli is consistent with the presence and activity of angiotensin-converting enzyme (ACE).
• These findings support the localization of functional ACE within the human glomerulus, providing a basis for further investigation into its role in renal diseases.