Vitamin D-regulated, ATP-dependent calcium transport by intestinal golgi vesicles during maturation in the rat

The developmental aspects of Calcium uptake by intestinal Golgi vesicles was determined using highly purified Golgi vesicles from enterocytes of suckling (2 wk old), weanling (3 wk old), and adolescent (6 wk old) rats. Calcium uptake by Golgi vesicles at all age groups represented transport into the intravesicular space as evident by temperature dependency and by calcium ionophore A23187-induced calcium efflux studies. Calcium uptake was driven by ATP at all age groups, however, maximal uptake at 15 min was significantly greater in Golgi vesicles of adolescent rats compared to mean values in Golgi vesicles of suckling rats (p < 0.01). Calcium uptake in the absence of ATP was minimal. The requirement for the adenine base and the hydrolysis of the β-γ-phosphodiester was tested by replacement of ATP in the incubation media by CTP and the nonhydrolyzable ATP analogue, adenylyl-(β-γ-methylendiphosphonate). Both agents had no stimulatory effect on calcium uptake. Calcium uptake was linear up to 40 s. Kinetic parameters of calcium uptake at free calcium concentrations of 0.04 to 1.0 ftM showed a maximal transport capacity of 0.99 ± 0.05, 0.55 ± 0.04, and 0.29 ± 0.03 nmol/mg protein/15 s for adolescent, weanling, and suckling rats, respectively. Km values were 0.16 ± 0.02, 0.12 ± 0.03, and 0.07 ± 0.02 μM for adolescent, weanling and suckling rats, respectively. Km and V_max values were significantly different between adolescent and suckling rats (p < 0.01). The calcium regulatory protein calmodulin has no effect on calcium uptake by Golgi vesicles. Vitamin D deficiency in all age groups decreased ATP-dependent calcium uptake. Administration of 1,25-(OH)₂ vitamin D3 8 h before death enhanced ATP-dependent calcium uptake in all age groups studied. This enhancement was the result of increase in maximal transport capacity of ATP-dependent calcium uptake. This study demonstrates a vitamin D-regulated ATP-driven calcium uptake by intestinal Golgi vesicles at all age groups including the suckling period. This transport system shows developmental patterns in regard to its kinetic parameters.