Cellular osmoregulation of the ark clam (Anadara kagoshimensis) hemocytes to hyposmotic media.

Many bivalve species are considered to be euryhaline organisms due to effective adaptation to fluctuations of environmental salinity. Cellular mechanisms responsible for tolerance to salinity changes remain unclear for bivalves despite this question being critically important for commercially cultured species frequently introduced into regions differing from natural habitat by salinity regime. In the present work laser diffraction method was used for the analysis of volume changes in hemoglobin-containing ark clam (Anadara kagoshimensis) hemocytes following hyposmotic stimulation. Hemocytes responded to hyposmotic shock (decrease of media osmolarity from 461 to 216 mОsm/L) by a rapid swelling up to 171.5 ± 15.2% of control level. At normal osmotic conditions (osmolarity 461 mOsm/L), hemocyte mean cellular volume (MCV) was 354.0 ± 24.4 fl and maximum MCV of hyposmotically swollen cells prior lysis was 555.5 ± 57.4 fl (at the osmolarity 194 mOsm/L). Ark clam hemocytes demonstrated volume recovery response following hyposmotic swelling. Regulatory volume decrease (RVD) reaction did not depend on hemoglobin confirmation status. Final MCV of swollen hemocytes at the end of experimental period of RVD in oxygenated and deoxygenated suspensions did not significantly differ.