Calcium Transport by Plasma Membranes of Enterocytes during Development: Role of 1,25-(OH)2 Vitamin D3

Abstract

ABSTRACT. Calcium transport across the intestinal enterocytes represents an entry process at the brush border membranes and an ATP-dependent exit process located at the basolateral membranes. Both processes exhibit developmental changes. The present studies were designed to define the role of vitamin D in calcium transport during maturation. Brush border and basolateral membranes from vitamin D-deficient suckling and adolescent rats were used to study calcium entry and exit. 1,25-(OH)2 vitamin D3 administration enhanced calcium entry at the brush border membranes of suckling and adolescent rats. The increase in calcium uptake in both age groups was secondary to an increase in maximal transport capacity (V,,,) rather than in K,. In suckling rat brush border membranes, 1,25-(0H)z vitamin D3 treatment increased the V, , , from 1.0 + 0.1 to 1.8 f 0.2 nmollmg protein17 s ( p < 0.01), whereas in adolescent rats, V, , , increased from 1.5 f 0.1 to 2.5 f 0.3 nmollmg protein17 s ( p < 0.01). K, values were not altered.Similarly, 1,25-(OH)2 vitamin D3 administration enhanced ATP-dependent calcium exit at the basolateral membranes of both suckling and adolescent rats. V, , , of ATP-dependent calcium uptake by basolateral membranes of suckling rats increased from 0.5 f 0.05 to 0.81 f 0.06 nmollmg protein120 s ( p < 0.01) whereas in adolescent rats, V , increased from 0.3 f 0.03 to 0.6 f 0.04 nmol/mg protein/ 20 s ( p < 0.001). K, values were not altered. The current studies indicate that 1,25-(0H)z vitamin D3 stimulates calcium entry and exit across the enterocytes during maturation. (Pediatr Res 24:338-341, 1988)

Intestinal Brush Border Calcium Uptake in Spontaneously Hypertensive Rats and Their Genetically Matched WKY Rats

“…The mucosa was scraped off with a glass microscope slide. BBM vesicles were isolated at first by sequential precipitation with 0.01 M MgC12 and differential centrifugation as described previously (18)(19)(20). To separate plasma membranes from adhering terminal web and microvillus core, we used potassium thiocyanate at the final step, according to the method of Hopfer et al (21).…”

In vivo effect of calcitriol on calcium transport and calcium binding proteins in the spontaneously hypertensive rat.

“…Thus, calbindin-D9K may participate in calcium transport at this level. Ghishan et al 39 in the rat and Takito et al 36 in the chicken reported that calcitriol administration enhanced calcium entry in the brush border membrane vesicles by increasing the maximum transport capacity (K^) but not the affinity (K^). An increase in the amount of calbindin-D9K at the brush border could explain these earlier observations.…”