Calcium and adenosine triphosphate binding to renal membranes

Area of Science:

• Biochemistry
• Cell Biology
• Nephrology

Background:

• Membrane-bound calcium plays a role in cellular functions.
• Understanding calcium binding mechanisms in kidney cells is crucial for nephrology research.

Purpose of the Study:

• To investigate the characteristics of calcium binding to renal membranes.
• To elucidate the role of ATP and other factors in this binding process.

Main Methods:

• Isolation of membranous structures from rabbit kidney cortex homogenates.
• Assessing calcium binding using radiolabeled calcium (45Ca) and ATP (32P, 14C).
• Evaluating the effects of various agents like ATP, Mg++, ITP, GTP, oxalate, p-chloromercuribenzoate, and mercaptomerin.

Main Results:

• Calcium binding to renal membranes is enhanced by ATP and Mg++.
• Oxalate does not augment calcium binding, unlike in nerve and muscle preparations.
• Inhibition by p-chloromercuribenzoate and mercaptomerin suggests a protein-mediated process.
• (32)P-labeled ATP binding increases with calcium addition, with a 2:1 ratio of (32)P to (45)Ca bound.
• Azide inhibition and ADP-succinate substitution failure distinguish this from mitochondrial calcium binding.

Conclusions:

• Calcium is metabolically bound to renal membranes, associated with membrane phosphorylation.
• This calcium binding may influence renal membrane conformation and permeability.
• Renal membrane stability appears to require metabolic participation and calcium ions.