Thyroid hormones modulate zinc transport activity of rat intestinal and renal brush-border membrane

Thyroid hormone status influences the Zn2+ and metallothionein levels in in testine, liver, and kidney. To evaluate the impact of thyroid hormones on Z n2+ metabolism, Zn2+ uptake studies were carried out in intestinal and rena l brush-border membrane vesicles (BBMV). Steady-state Zn2+ transport in int estinal and renal cortical BBMV was increased in hyperthyroid (Hyper-T) rat s and decreased in:the hypothyroid (Hypo-T) rats relative to euthyroid (Eu- T) rats.: In both the intestinal, and renal BBMV, Hyper-T rats showed a sig nificant increase in maximal velocity compared with Eu-T and Hypo-T rats. A pparent Michaelis constant was unaltered in intestinal and renal BBMV prepa red from the three groups. Fluorescence anisotropy of diphenyl hexatriene w as decreased significantly:in intestinal and renal brush-border membrane (B BM) isolated from Hyper-T rats compared with Hypo-T and Eu-T rats. A signif icant reduction iri the microviscosity and transition temperature for Zn2uptake in intestinal and renal BBM from Hyper-T rats is in accordance with the increased fluidity of these BBMs. These findings suggest that the incre ased rate of Zn2+ transport ih response to thyroid hormone status could be associated with either an increase in the number of Zn2+ transporters or an increase in the active transporters due to alteration in the membrane flui dity. Thus the thyroid hormone-mediated change in membrane fluidity might p lay an important role in modulating Zn2+ transport activity of intestinal a nd renal BBM.