Hymenolepis diminuta: Unstirred layer thickness and effects on active and passive transport kinetics

Abstract

The present study was designed to investigate the effects of unstirred water layers on the apparent influx kinetics of glucose, galactose, and alanine uptake by Hymenolepis diminuta incubated in vitro. Kinetic curves obtained, using a series of stirring rates, for influx of each solute were separated into a mediated component describing a rectangular hyperbola and being characterized by apparent K′ t and J′ max values, and a linear component characterized by an apparent passive permeability coefficient ( K′ d ). Stirring the incubation medium from zero up to 2540 rpm reduced the unstirred layer thickness from 251–377 μm to 9–35 μm depending on the probe molecule used. Decreasing the unstirred layer thickness decreased the apparent K′ t for the influx systems toward the “limiting” values ( K t ), which were obtained by extrapolation. The K t values for alanine, glucose, and galactose were (m M) 0.1, 0.21, and 0.64, respectively. J′ max was not altered significantly by stirring but K′ d was increased for each solute. For a given incremental change in the unstirred layer thickness, the decreases in K′ t were in direct proportion to their J t ́ max . Theoretically expected influx values based on K t , J max, and d (unstirred layer thickness) and the experimentally observed influx values did not always agree, the difference being discussed in terms of changes in surface area and removal of mucus or components of the host's immune response from the worm surface at the higher rates of stirring. The data suggest that the flux of alanine, glucose, and galactose across the unstirred layer is the normal rate-limiting step in trans-brush-border transfer of these solutes by H. diminuta when less than saturating concentrations are present in the environment.