Absence of relationship between the postnatal development of ileal active taurocholate transport and microvillus membrane fluidity.

Concurrent measurements of ileal microvillus membrane vesicle transport and fluorescence anisotropy were performed on magnesium precipitated membranes from rats of various ages during the third postnatal week. At age 14 and 18 days, taurocholate uptake was comparable in the presence of NaCl and KCl gradients. At age 20 days, a 'sodium effect' and at age 21 days an 'overshoot' were observed in the presence of NaCl gradients. No significant change in fluorescence anisotropy was observed between postnatal days 14 and 21. These studies suggest it is unlikely that changes in microvillus membrane fluidity modulate the postnatal development of ileal active bile salt transport.