Studies on arthropod cuticle—XIII: The penetration of dissolved oxygen and electrolytes in relation to the multiple barriers of the epicuticle

Abstract

Using isolated cuticles of Sarcophaga larvae, the penetration of oxygen was measured polarographically and the penetration of ions was studied by complex impedance. Comparison of data from normal and treated cuticles shows that the heterogeneous epicuticle contains at least three distinct components. The ionic barrier is the exceedingly thin outer epicuticle which is resistant to a variety of hot solvents, detergents, and acids but is disrupted by alkali. The water barrier is located in the thicker inner epicuticle (appears to be the outer portion thereof), and is disrupted by organic solvents. The site for control of asymmetrical penetration is in the inner portion of the inner epicuticle, and is not disrupted by hot solvents. A small amount of data on other species suggests that in general the electrolyte barrier will be found to be distinct from the water barrier in insect cuticles. It follows that one of the reasons for the superposition of numerous sublayers in the insect cuticle is that different sublayers are barriers to different groups of chemicals. Brief note is made of the fact that the electrical properties of cuticle were found to be complicated, and to include rectification, polarization effects, and even bimodal polarization peaks which imply transient energy changes.