STUDIES ON MEMBRANE TRANSPORT V. TRANSPORT OF LONG CHAIN FATTY ACIDS IN HYMENOLEPIS DIMINUTA (CESTODA)

¹ Department of Biology, Rice University, Houston, Texas 77001

1. The uptake of ¹⁴C-palmitate by Hymenolepis diminuta has been shown to occur via a mediated process at concentrations of up to 4.5 mM palmitate. Entry of palmitate by diffusion is not thought to be significant under present conditions.

2. Fatty acids containing less than 12 carbon atoms and substances other than fatty acids did not inhibit palmitate uptake. Laurate, at all concentrations, stimulated uptake, while saturated fatty acids with up to 24 carbon atoms inhibited uptake to varying degrees. Three of the four unsaturated fatty acids tested stimulated palmitate uptake when present at concentrations equal to that of palmitate and inhibited uptake when their concentrations were increased. All saturated fatty acids that affected palmitate uptake were found to be partially competitive inhibitors or stimulators.

3. A pH optimum was detected for palmitate uptake.

4. The effects of bile salts on palmitate uptake were investigated, but the role of bile in the transport of palmitate could not be elucidated.

5. The differences in palmitate uptake following dilution of 2 mM and 10 mM palmitate stock solutions are thought to reflect the physical properties of fatty acid solutions. It is postulated that 10 mM dilutions of palmitate contained either a greater number of, or larger, aggregated molecules than were present in 2 mM dilutions. It is considered that enhancement of palmitate uptake is related to the presence of these molecular aggregates.