AJP - Regulatory, Integrative and Comparative Physiology, Vol 233, Issue 5 198-R207, Copyright © 1977 by American Physiological Society
Water transport in perfused scorpion ileum
G. A. Ahearn and N. F. Hadley
Water transport in desert scorpion ileum involves two independent transfer
pathways operating in parallel: 1) paracellular flow occurs through
intercellular spaces in response to transmural osmotic or ionic gradients;
and 2) transcellular water transport occurs across apical and basal cell
membranes in response to a basal, energy-requiring sodium efflux process.
The tissue exhibits no osmotic rectification over the range of
transepithelial osmotic gradients imposed (Lp = hydraulic conductivity), Lp
= 95 x 10(-7) cm - s-1 - atm-1), but displays apparent asymmetric ion
permeability in response to transmural ion gradients, as determined by
codiffusional water movements across the preparation. Osmotic permeability
((Pos), Pos = 1.13 x 10(-3) cm - s-1) of the tissue exceeds diffusional
permeability ((Pd), Pd = 1.45 x 10(-5) cm - s-1) by almost two orders of
magnitude. In the absence of osmotic or hydrostatic pressure gradients,
transmural water transport requires cellular metabolism, is
sodium-dependent, is inhibited by potassium, and produces an apparent
strongly hypotonic absorbate. This water transport process appears to be
adaptive, as scorpion dehydration results in alterations of luminal ion
concentrations that favor increased net flow of water to the hemolymph.
