The effect of dimethylsulfoxide on the tegumental brush border of the cestode Hymenolepis diminuta

Dimethyl sulfoxide (DMSO), commonly used for cryoprotection or for the solvation of cytoskeleton-modifying drugs, causes changes in the topology of the plasma membrane of the tegumental brush border in the tapeworm Hymenolepis diminuta; however, relatively long exposures or high concentrations are required. In tapeworms treated with DMSO concentrations of ≥1% in the present study, the interaction of the tegumental surface membrane with the underlying cytoskeleton may have been disrupted at focal points in the brush border, resulting in a partial loss of the membrane anchoring required for the structural integrity of the brush border. Blebbing of the tegumental surface was prominent only after exposure to 1% DMSO for 20 h in vitro culture with RPMI 1640, and vesiculation of the membrane along the microvillar (microtriche) shafts, which may have been related to the in vitro conditions, was amplified by the presence of concentrations of ≥1% DMSO in the incubation medium. The tegumental response to DMSO was not uniform but regional, consistently appearing to be more prevalent on the distal aspects of each proglottid rather than on the edge proximal to the scolex. Blebbing and vesiculation were not seen on the basal aspect of the tegument, including the basal ectocytoplasmic plasma membrane, the perikarya, and the internuncial processes. Microvillar core bundles of actin microfilaments persisted following 8 h in vitro exposure to all three concentrations of DMSO tested (0.1%, 1%, 5%); however, only in tapeworms that were treated in vitro with 5% DMSO for ≥ 8 h did core microfilament bundles appear to lose the rigidly straight and parallel organization characteristic of control tapeworms that were incubated either in the absence of DMSO or with 0.1% DMSO. Other components of the brush border cytoskeleton (i.e., microvillar caps, junctional tubules, and tunics) appeared unaffected by DMSO except at foci where blebbing occurred. These data suggest that in vitro concentrations of <1% DMSO have little observable effect on the anchoring of the tegumental surface membrane to the underlying cytoskeleton or the organization of the microfilamentous cytoskeleton of the brush border microvilli. The present investigation thus provides baseline data on DMSO-induced artifact for future studies that require the use of DMSO but do not focus on its effects.