DIVALENT CATION AND pH DEPENDENCE OF RAT INTRINSIC FACTOR ACTION IN EVERTED SACS AND MUCOSAL HOMOGENATES OF RAT SMALL INTESTINE*

In 1959 it was reported in these pages (1) that hog intrinsic factor concentrate enhanced the up- take of radioactive vitamin B12 (Co60-B12) by everted sacs of rat small intestine in the cold. This enhancement was significantly reduced in the absence of calcium and was reversible to a significant degree by disodium ethylenediamine tetraacetate dihydrate (EDTA) (1), suggesting that intrinsic factor action was calcium-dependent. Disodium EDTA reduced the enhancing effect on radio-Bl2 uptake of rat intrinsic factor in loops of small intestine in a living rat; calcium EDTA was without such inhibitory effect (2). Other workers, however, threw doubt on the calcium dependence of intrinsic factor action. They re- ported that gastrectomized rats fed radio-B12 bound to rat gastric juice plus large amounts of disodium EDTA (3, 4), and normal rats fed radio-B12 plus disodium or tetrasodium EDTA (5), had normal radio-B12 absorption. These findings, taken with the fact that the in vitro studies did not demonstrate total loss of the effect of intrinsic factor on depletion of calcium, left the concept of the calcium dependence of intrinsic fac- tor action in doubt.