Extraction model of the longitudinal flagellum of Ceratium tripos (Dinoflagellida): reactivation of flagellar retraction

The mechanism of retraction of the longitudinal flagellum of Ceratium tripos was studied by making extracted models of the flagellum. Non-detergent models extracted in low ionic strength medium containing 1 M-glucose, 10 mM-EDTA, and 50 mM-Tris X HCl buffer (pH 8.0), retracted when Ca2+, Mg2+, Ba2+, Sr2+, Mn2+ or Cd2+ was applied locally with a glass capillary. A demembranated model of the flagellum was made with an extraction medium containing 0.8-1.0 M-glucose, 20 mM-Tris-acetate (pH 7.8), 2 mM-EGTA, 5–7 mM-MgSO4, 0.1 M-potassium glutamate and 0.1% Triton X-100. The model required a concentration of Mg2+ of a few mmol/l for successful reactivation of both retraction and undulation, and about 0.1 M-potassium glutamate (or sodium glutamate) for reactivation of undulation. Neither type of motion of the models could be reactivated above 35 degrees C. Ca2+ induced the retraction at pCa 5.5 or less. In addition to Ca2+, Mn2+, Ba2+, Sr2+ and Cd2+ also induced retraction but Mg2+, La3+ or Tb3+ did not. Although ATP was required for undulation, it was not required for retraction. Co-incubation with hexokinase to remove contaminating ATP did not suppress the retraction. The potent ATPase inhibitor, orthovanadate, inhibited undulation at 10 micron but did not inhibit retraction even at 2 mM. SH blockers, N-ethylmaleimide and dithio-bis-nitrobenzoic acid strongly suppressed undulation but had no effect on retraction. Calmodulin inhibitors, trifluoperazine and chlorpromazine, also had no effect on retraction. These data indicate that undulation is generated by a 9 + 2 microtubular axoneme using energy released by hydrolysis of ATP and that retraction can be induced by Ca2+ without a requirement for ATP.