Calcium and Strontium in Rat Small Intestine Their Fluxes and Their Effect on Na Flux

Abstract

ABSTRAGT Studies have been carried out on movements of Ca and Sr ions in rat small intestine, using the in vivo preparation developed by Curran and Solomon (5). In the concentration range of 0 to 25 raM, Sr flux appears to be passive, though restricted. Ca transport may not, however, be ascribed to passive independent movement of these ions since at higher concentrations (12.5 and 25 raM) Ca return from blood to intestinal lumen increases more than expected. An apparent diffusion coefficient of Ca and Sr ions in the membrane has been calculated and the influence of negative charges within the membrane on cation diffusion has been examined in a semiquantitative manner.Both Ca and Sr ions exercise a drastic effect on active Na absorption from intestine and on concomitant passive water movement. From 0 to 1 mM, Ca and Sr ions cause a sharp increase in Na and water efflux from the lumen. This rising phase is interpreted in terms of combination of the divalent cation with the Na carrier system following Michaelis-Menten kinetics. At concentrations higher than 1 mM, the effect of Ca and Sr ions is reversed and Na and water absorption decreases slowly as Ca or Sr concentration is increased. This failing phase is ascribed to a non-specific Ca effect which produces a general "stiffening" of the membrane.T h e present study is c o n c e r n e d with cation t r a n s p o r t across the small intestinal m u c o s a in the rat---specifically with C a a n d Sr fluxes a n d the effect exercised b y these ions on N a flux. T h o u g h the intestinal a b s o r p t i o n of C a has long b e e n studied (1-4), no specific m e c h a n i s m s of a b s o r p t i o n h a v e yet been d e m o n s t r a t e d . T h e e x p e r i m e n t s comprise an in vivo study of the a b s o r p -

Jejunal and ileal absorption in patients with chronic renal disease. Effect of 1alpha-hydroxycholecalciferol.

“…The flux out of the lumen was higher with the 5-than with the 1-mM calcium test solutions, which is expected. The flux into the lumen is also higher with the 5-than with the 1-mM calcium solution; although difficult to explain, this same observation has been made previously by Dumont et al (34) and by Wasserman and Kallfelz (35), and these authors have speculated on its meaning.…”

Strontium and Bone

“…Some authors suggested that in contrast to calcium, strontium is absorbed entirely via passive diffusion, i.e., paracellular transport. (13,14) However, Papworth et al proposed two routes of entry for the element: carrier-mediated and diffusionmediated. (15) With the exception of infants, it can generally be stated that strontium is absorbed to a lower extent than calcium, the strontium/calcium absorption ratio being ∼0.50.…”

Different effects of bile and sodium taurocholate on mucosal calcium accumulation and calcium absorption in rats.

“…In contrast, the mucosal calcium and 45Ca contents in the jeju num were increased in the presence of bile and Na taurocholate. This partly reflect ed the type of calcium transport affected, i.e., passive or energy-independent trans port, which is predominant in the jejunum (22). This marked increase in mucosal calcium may also be explained by a longer transit time in the jejunum as com pared to the transit through the duodenum (23) in the in vivo condition.…”