Boettger, S.A.*; McClintock, J.B.: The effects of organic and inorganic phosphate on muscle contraction and acetyl cholinesterase activity of the nearshore echinoid Lytechinus variegatus.

Lytechinus variegatus is a common nearshore sea urchin that is exposed to phosphate pollutants. Sea urchins were collected in April, 2000 from Saint Joseph’s Bay in the northern Gulf of Mexico. Individuals were divided into a control (artificial sea water), sea water containing three concentrations of inorganic (sodium phosphate); or three concentrations of organic (triethyl phosphate) phosphate. Individuals were maintained for an 8-week period, dissected and the Aristotle’s lantern retractor muscles extracted individually. Each muscle was attached to a strain gage, stimulated electrically, and muscle contractions (g force/mm muscle length) recorded. When compared to the control group, force of contraction increased significantly in individuals maintained in increasing concentrations of both phosphates. Following the direct coloring thiocholine assay, acetyl cholinesterase activity was assessed by embedding and staining retractor muscles from the Aristotle’s lantern, tube-feet, and gut, and counting the occurrence of fully-stained motor endplates/mm2 . Acetyl cholinesterase activity in these same muscles was also assessed through a colorimetric assay. The number of fully-stained motor endplates and the enzymatic activity of acetyl cholinesterase decreased in individuals maintained in increasing concentrations of organic phosphate when compared to the control group. No change occurred in individuals exposed to inorganic phosphate. These results indicate that while phosphate exposure has a significant effect on muscle contraction in Lytechinus variegatus, the inhibition of acetyl cholinesterase, an enzyme critical to muscle relaxation, can only be a potential contributing factor in individuals maintained in organic phosphate.