Cell volume regulation in the trypanosomatid Herpetomonas samuelpessoai

Herpetomonas samuelpessoai was submitted to hypo- and hyper-osmotic shocks in buffer and culture medium. Cell volume was evaluated with an electronic particle counter and by the transmission of a parasite suspension measured at 540 nm with a spectrophotometer. Cell volume changes after osmotic shock were transient, parasites being able to completely restore cell volume to the original values in culture medium but not in buffer. The kinetics of transmittance changes closely resembled that of volume variations. The volume regulatory increase (but not decrease) was dependent on extracellular K concentration and strongly influenced by the parasite growth phase. Evidence is presented supporting the idea that changes in transmission values can be linearly correlated to mean cell volume variations in free-floating cells.