Schistosoma mansoni: Measurement of Na + ion activity in the tegument and the extracellular spaces using ion-selective microelectrodes

Abstract

Ion-selective microelectrodes were used to measure sodium ion activity ( a Na) in the tegument and interstitial spaces in adult male Schistosoma mansoni. In RPMI 1640, a Na averaged 31 ± 13 m M in the tegument, a value significantly less than that in the bathing medium. In the interstitial spaces, it averaged 72 ± 17 m M, a value nearly the same as that in the bathing medium. In hypo- or hyperosmotic media, a Na in the interstitial spaces varied by a value commensurate with change in a Na in the medium, but a Na in the tegument was changed by only a small amount. Monensin (10 μ M), low temperature (20 C), and ouabain (0.3 to 10 μ M) all caused significant increases in a Na in the tegument. Hypo- and hyperosmotic media produced initial weight changes followed by gradual recovery back toward original weights. It is concluded that the schistosome is a volume regulating osmoconformer with osmolality of the extracellular fluid approximating that of the bathing medium, but that within the tegument of the parasite, Na + concentration is controlled by active transport processes.