Effect of divalent cations and pH on intrinsic factor-mediated attachment of vitamin B<sub>12</sub> to intestinal microvillous membranes

Iain L. Mackenzie; Robert M. Donaldson

doi:10.1172/JCI107060

Effect of divalent cations and pH on intrinsic factor-mediated attachment of vitamin B₁₂ to intestinal microvillous membranes

Iain L. Mackenzie and Robert M. Donaldson Jr.

Published September 1, 1972 - More info

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Abstract

Calcium, but not other divalent cations, is required for optimal uptake of intrinsic factor-bound ⁵⁷Co-labeled cyanocobalamin (IFB₁₂) by microvillous membranes isolated from hamster ileal-absorptive cells. Chelation of divalent cations by disodium ethylenediaminetetraacetate (EDTA) promptly removes IFB₁₂ previously attached to microvillous membranes. High concentrations of CaCl₂ or MgCl₂ also markedly inhibit membrane uptake of IFB₁₂ and rapidly remove previously attached IFB₁₂. Similarly, reduction of pH to below 5.4 prevents membrane attachment of IFB₁₂ and removes virtually all IFB₁₂ already bound to microvillous membranes. The effects of calcium depletion, increased salt concentrations, and acidification on membrane uptake of IFB₁₂ were completely reversible. These findings are consistent with the concept that the formation of calcium salt bridges is essential for attachment of IFB₁₂ to the ileal-absorptive surface.