Binding strength, potassium-calcium

Proteins bind these four cations with strengths that depend on the size of the cation and its charge. The higher the charge, the better the cation binds the binding of potassium and sodium ions is poorer than that of magnesium and calcium ions. The size is also important and a protein often provides a pocket of the correct size so that it can distinguish between... 

While most of the discussion about acidity and bone loss focuses on calcium, the same study revealed that bone is also a reservoir for sodium and potassium, and its surface has receptor sites that normally bind with sodium, potassium, and hydrogen. When the body becomes too acidic, hydrogen bumps sodium and potassium off the bone surface to buffer the systemic acidity, further depleting the bones of minerals that are essential for their health and strength. 

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