WILL, M.C.; BARNETT, A.R.; RIDGWAY, R.L.*; Seattle Pacific Univ.; Seattle Pacific Univ.; Seattle Pacific Univ.: Inhibition of Molluscan Hemocyte Motility by a Calmodulin Antagonist

Hemocytes serve as a multipurpose cellular defense system in molluscs, circulating in the hemolymph until activated by tissue damage or infection. Activated hemocytes of the pond snail Lymnaea stagnalis change from spherical cells into highly motile phagocytes and then into aggregating fibroblast-like cells. Correlated with these morphological stages are characteristic shifts in the organization of cytoskeletal elements. Previously, we have shown that these morphological changes are sensitive to reduced concentrations of extracellular Ca²⁺, suggesting Ca²⁺-dependent regulatory pathways may be affected. We examined this possibility by exposing populations of activated hemocytes to the calmodulin inhibitor W-7 (N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide HCl) or its inactive, dechlorinated analogue (W-5). Hemocytes fixed after 5 min exposure to 100 uM W-7 showed no significant differences in either motility or cytoskeletal (microfilament, microtubule) organization relative to controls. After 15 min, however, the percentage of motile cells in preparations exposed to W-7 was less than one-third that of control preparations; after 25 min, all cells treated with W-7 appeared non-motile. Both microtubular and microfilament organization appeared compromised in cells treated with W-7. In contrast, cytoskeletal organization was unaffected by W-5 exposure and the percentage of motile cells in preparations exposed to W-5 was actually greater than that of controls at the 15 and 25 min fixation times. These results strongly suggest a role for Ca²⁺-calmodulin in regulating cytoskeletal organization and cell motility during hemocyte activation in molluscs. (Supported in part by a SPU Faculty Research Grant to RLR.)