Osmolality and electrolyte concentration of hemolymph and the problem of ion and volume regulation of cells in higher insects

• 1.1. The study was carried out on 22 species of insects from 5 orders. The osmolality of their hemolymph varied from 319 to 421 mOsm/kg H₂O, concentration of Na⁺ 4.6 to 118 mM/l, K⁺ 6.3 to 73mM/l, Ca²⁺ 3.6 to 12.9 mM/l, Mg²⁺ 2.3 to 76 mM/l. The most abundant cation in the hemolymph of insects from higher orders is either K⁺ or Mg²⁺.
• 2.2. In the muscles of lower and higher insects K⁺ is usually within 80–120 mM/kg wet wt.
• 3.3. Most Ca²⁺ and Mg²⁺ in hemolymph is bound with protein and low molecular anions, concentration of free Ca²⁺ is 0.9-2.1mM/l Mg²⁺ 3.7–8.0 mM/l.
• 4.4. It is concluded that, in insects, potassium hemolymph, cell volume regulation and accumulation of ions in the cell, are ensured by an increased osmolality of hemolymph due to a high percentage contribution of low molecular organic substances which are retained in the hemolymph due to the absence of filtration apparatus in the Malpighian tubules.