Induction of deflagellation by various local anesthetics in Chlamydomonas reinhardtii Dangeard (Chlamydomonadales, Chlorophyceae)

Dibucaine, a local anesthetic, is known to induce flagellar excision in Chlamydomonas reinhardtii. Herein, we investigate whether other local anesthetics have similar effects. Tetracaine, bupivacaine, procaine, and lidocaine also caused flagellar excision, although their potencies were lower than that of dibucaine. Bupivacaine, procaine, and lidocaine induced a morphological change in flagella from a rod-like shape to a disk-like shape before flagellar excision. Except for lidocaine, these local anesthetics caused cell-wall shedding in addition to flagellar excision. The anesthetics in order of their median effective concentration (1-h EC₅₀) for flagellar excision are as follows: dibucaine (1.37 × 10^-5 M) < tetracaine (3.16 × 10^-5 M) < bupivacaine (4.25 × 10^-4 M) < procaine (2.02 × 10^-3 M) < lidocaine (3.61 × 10^-3 M). In all cases, Ca²⁺ depletion from the solution inhibited flagellar excision. However, Ca²⁺-channel blockers, IP3 receptor antagonists, and inhibitors of phospholipase C did not prevent excision. We suggest that the local anesthetics induce flagellar excision by increasing the fluidity of the flagellar/cell membrane, thereby allowing extracellular Ca²⁺ to flow into the cell and cause flagellar excision.