Freshwater stonefly larvae take up sodium and chloride ions from low concentrations in water and concentrate them into haemolymph. The ions are transported by mitochondria rich cells (MRITCs) which are easily identified by their windows in the cuticle. Sodium uptake is generally inhibited at low pH but a few species of stoneflies live in acid waters. Acid tolerance is associated with presence of caviform or bulbiform MRITCs while nymphs possessing only the more common coniform cells are sensitive to acid conditions.
The intracellular concentrations of Na, K, Cl and P in coniform cells of Perla bipunctata and bulbiform cells of Protonemura meyeri have been measured by X-ray emission analysis in a scanning electron microscope (SEM). Both bulbiform and coniform cells respond to low pH by increasing the concentrations of P and of the ions Na, K and Cl, but the ionic concentrations in coniform cells soon decline at low pH and the cells fail, while bulbiform cells maintain their ionic concentrations down to a lower pH. The major transport systems on the apical and baso-lateral membranes have been identified from the effects of ions and drugs, applied to the two surfaces, on the intracellular concentrations of ions. Bulbiform and coniform cells contain similar transport systems but differ quantitatively in response to low pH.
Potts, W. T. W. and Bricknell, I.
"The Ionic Composition of Ion Transporting Cells in Stonefly Nymphs,"
Scanning Microscopy: Vol. 6
, Article 25.
Available at: https://digitalcommons.usu.edu/microscopy/vol6/iss1/25