Functional roles of luminal sodium and potassium in water transport across desert scorpion ileum

Abstract

IN terrestrial insects the rectum is a major site of fluid absorption and is, therefore, important in the physiological control of water balance. Water absorption in the insect rectum occurs against osmotic gradients greater than 300 mosmol 1⁻¹ and apparently in the absence of net ion movements from lumen to haemolymph^1,2. Evidence suggests that net water flow from the rectal lumen to haemolymph results from increases in intercellular space osmotic pressure due to the transport across lateral cell membranes of recyclable intracellular solutes^3,4. Little is known about the mechanism of water transport in the insect gut anterior to the rectum nor about gastrointestinal processes involved in water regulation in other terrestrial arthropods. Scorpions are ideal organisms for measurements of arthropod deal transport because this part of the gut extends nearly the entire length of the tail and can be isolated for in vitro perfusion. We present here preliminary information on a sodium-dependent, potassium-inhibited water transport mechanism in the ileum of the desert scorpion Hadrurus arizonensis.