Transport across the crop wall in Helix aspersa

Stenhouse, John (1995) Transport across the crop wall in Helix aspersa. PhD thesis, University of Glasgow.

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Abstract

This project was carried out to elucidate the ion transport properties of the crop of Helix aspersa. An examination was made of each of the following; changes in ion concentrations; the effects of inhibitors; and glucose and amino acid transport. Short circuit current and transepithelial resistance were measured in order to achieve this. The major findings of the study were: The most unusual feature of the crop epithelium is the fact that the short circuit current (SCC) could be either positive or negative under standard control conditions. After a period of stabilisation, under standard bathing conditions, the crop was found to have a transepithelial potential difference that could be either positive or negative with respect to the basal side. The mean transepithelial resistance, under standard bathing conditions, was 67.9 (+/-3.1) ohm cm2 (n=158). The magnitude of the mean resting potential difference, short circuit current and resistance were consistent with those of a classic "leaky" epithelium. Sodium was required for the maintenance of a large transepithelial potential difference. The SCC became significantly more negative when potassium was removed from both sides, or from the apical side only. Upon the substitution of chloride on both sides of the tissue there was a significant change in the sec, with the basal side becoming more positive. The removal of magnesium was tested under sodium free as well as sodium plus chloride free condition as control. Calcium removal was tested under standard and sodium plus chloride free conditions. Ouabain, which has been universally accepted as inhibiting the Na+/K+ATPase, was highly effective when added basally at a concentration of 10mM. Piretanide, a loop diuretic related to the compounds furosemide and bumetanide, is also an inhibiter of Na+/K+/2C1- co-transport. Use of sodium thiocyanate, an inhibitor of chloride transport, resulted in the basal side becoming significantly more positive only when added basally. There was no significant change in the SCC when added apically. The crop epithelium seems to have potassium conductance channels on both sides of the tissue. The barium ion is a known inhibitor of potassium channels and when it was added to each side of the tissue in turn the SCC changed significantly. Amiloride made the SCC significantly more negative when added at a concentration of 0.5mM to the apical side of the epithelium. The crop epithelium has the ability to transport organic substances, for example D-glucose and glycine. D-glucose and glycine used different carriers, these having different saturation concentrations. There was no competitive inhibition taking place, as was illustrated by the outcome of the addition of firstly a maximal concentration of either D-glucose or glycine apically and then of the other substrate apically, which brought about a further change in the short circuit current. (Abstract shortened by ProQuest.).

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Richard Burton
Keywords: Plant sciences
Date of Award: 1995
Depositing User: Enlighten Team
Unique ID: glathesis:1995-71675
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 17 May 2019 09:31
Last Modified: 17 May 2019 09:31
URI: http://theses.gla.ac.uk/id/eprint/71675

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