AJP - Regulatory, Integrative and Comparative Physiology, Vol 270, Issue 5 1037-R1043, Copyright © 1996 by American Physiological Society
Thermal modulation of channel catfish intestinal dimensions, BBM fluidity, and glucose transport
K. L. Houpe, C. Malo, P. B. Oldham and R. K. Buddington
Department of Physiology, University of Montreal, Quebec Canada.
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).
