Chemical constituents of haemolymph and tissue in Telea polyphemus Cram. with particular reference to the question of ion binding

Abstract

Normal neuromuscular function in those insects with high extracellular fluid potassium concentrations has prompted theories which state that the tissue environment is either protected by a sheath which serves as a diffusion barrier, or that the physiologically active (ionized) potassium is present in much lower concentration than the total measured, because a large fraction is ‘bound’. The present study was designed to test both chemically and physiologically the possibility that ion binding occurs in haemolymph. Analyses of the major haemolymph constituents in Telea polyphemus Cram. revealed a pattern similar to other Lepidoptera, the principal features being a high potassium, high magnesium, low sodium, and a low chloride concentration. Heart and wing muscle analyses indicated about twice as much potassium intracellularly as extracellularly, but there was no sodium gradient. Haemolymph ultrafiltration demonstrated that between 15 and 20 per cent of calcium and magnesium were bound to macromolecules that did not pass the ultrafilter, but no binding of either potassium or chloride was apparent. Electrophoretic analysis indicated that the principal protein migrated like an α-2-globulin, a protein with known low binding capacity. Haemolymph osmotic pressure measured with a physical method was about twice the value determined with the red cell osmometer technique, due to the rapid passage of osmotically active particles, as well as water, across the red cell membrane. These particles are probably amino acids, but they do not carry any measurable potassium with them into the red cell, indicating that even if they do serve to some extent as anions in haemolymph the complex with potassium is not sufficiently tight to be called ‘bound’. Trans-membrane resting potentials of skeletal and heart muscle determined with the micro-electrode technique were in the range predicted from the cellular and haemolymph concentrations of potassium. Heart muscle action potentials ranged from 30 to 50 per cent of the resting value and in no instance exhibited ‘overshoot’. The depression in excitability of frog skeletal muscle exposed to insect haemolymph was similar to that measured in control muscles exposed to Ringer's solution with equivalent potassium concentrations. Since each of these physiological measurements is dependent solely on the concentration of ionized potassium, it may be inferred that no haemolymph potassium is in ‘bound’ or un-ionized state.