Permeation and Membrane Transport in Animal Parasites: Permeation of Urea into Cestodes from Elasmobranchs

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Abstract
A kinetic study of the entry of urea into Calliobothrium verticillatum revealed that simple diffusion is the mechanism of permeation. Urea permeation is a direct linear function of its concentration in the external medium. The Q10 of the process is 1.5 at 0-10[degree]C and 1.4 at 10-21[degree]C. Equilibrium is reached in 60-90 minutes. The rate of leakage of urea from the worm is comparable to its rate of entry. The rate of exchange between worm and medium closely approximates the rate of entry. Alteration of pH between 6.0 and 8.0 or addition of glucose does not affect the permeation rate.