Dietary lipid and intestinal brush border membrane phospholipid fatty acid composition and glucose transport of channel catfish.

Although the influences of dietary carbohydrate and protein on intestinal brush border membrane functions are well known, the responses to different dietary lipids are less clear, particularly for ectotherms. Therefore, we examined intestinal brush border membrane phospholipid fatty acid composition and rates of glucose transport of catfish fed two diets with different fatty acid profiles. Intestinal brush border membranes of fish fed a diet containing stearic acid had higher concentrations of monoenes, dienes, and trienes but were lower in polyenes and had a lower unsaturation index than those of fish fed a diet with menhaden oil. Rates of glucose transport at low, mid, and high temperatures were higher for intact tissues and vesicles prepared from the brush border membrane of fish fed the stearic acid diet. Our findings indicate that dietary lipids influence intestinal brush border membrane fatty acid composition and the relationship between temperature and rates of glucose transport. However, we can not exclude the possibility that dietary lipids can induce changes in transporter site densities and/or the physical characteristics of membrane microdomains in which the transporters might reside.

Thermal modulation of channel catfish intestinal dimensions, BBM fluidity, and glucose transport.

In light of the direct influence of temperature on metabolic rates and dietary loads of ectotherms, intestinal responses were evaluated by measuring 1) dimensions, 2) transapical initial rates of transport using intact tissues and brush-border membrane vesicles (BBMV), and 3) BBMV fluidity using two size groups of channel catfish (Ictalurus punctatus) acclimated to different water temperatures. Intestines of larger fish at 15 degrees C were 23% longer and 61% heavier than those at 30 degrees C. Regardless of assay temperature, rates of glucose uptake by fish held at 30 degrees C relative to those at 15 degrees C were twofold higher for intact tissues and over fivefold higher for BBMV. Although rates of PBMV transport were higher for smaller fish, adaptive responses were greater for larger fish. Temperature coefficients (Q10S) for BBMV transport were higher between 5 and 15 degrees C (3.5-4.5) relative to 15 to 35 degrees C (1.9-2.0) and may be partly related to the inability of catfish held at low temperatures to adjust apical membrane fluidity. Our findings indicate that 1) cold-acclimated catfish maintain transport capacities by increasing intestinal dimensions, 2) high acclimation temperatures increase rates of uptake by as yet unknown mechanisms, 3) thermal modulation of transport varies among species and nutrients, and 4) adaptive responses of ectotherms are different from those of homeotherms).