Biophysical effects of the natural product euplotin C on the Paramecium membrane.
The effect of euplotin C--a cytotoxic secondary metabolite produced by the protist ciliate Euplotes crassus--on the voltage-dependent Ca(2+) channel activity was studied in a single-celled system by analyzing the swimming behavior of Paramecium. When the intraciliary Ca(2+) concentration associated with plasma membrane depolarization increases, a reversal in the direction of ciliary beating occurs, and consequently the swimming direction changes. The ciliary reversal duration is correlated with the amount of Ca(2+) influx. The present study demonstrates that the duration of continuous ciliary reversal (CCR), triggered by high external KCl concentrations, is longer in euplotin C-treated cells. Using selective Ca(2+) channel blockers, we demonstrate that euplotin C modulates Ca(2+) channels similar to the T- and L-types that occur in mammalian cells. Indeed, the increase of CCR duration significantly decreased when flunarizine and nimodipine-verapamil blockers were employed. Membrane fluidity measurements using a fluorescent dye, 6-lauroyl-2-dimethylaminonaphtalene (laurdan), indicated that membranes in euplotin C-treated cells are more tightly packed and ordered than membranes in control cells. Our data suggest that euplotin C enhances backward swimming in our unicellular model system by interacting with the ciliary Ca(2+) channel functions through the reduction of cell membrane fluidity.
Dipartimento per lo Studio del Territorio e delle sue Risorse (DIP.TE.RIS.), Università di Genova, Corso Europa 26, 16132, Genoa, Italy. ramoino@dipteris.unige.it
Paola
P
Ramoino
Fernando
F
Dini
Paolo
P
Bianchini
Alberto
A
Diaspro
Graziano
G
Guella
Cesare
C
Usai
D000704:Analysis of Variance; D016880:Anisotropy; D001703:Biophysics / Q000379:methods; D002104:Cadmium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects* / Q000648:ultrastructure; D004305:Dose-Response Relationship, Drug; D008564:Membrane Potentials / Q000187:drug effects; D009532:Nickel / Q000494:pharmacology; D010247:Paramecium / Q000166:cytology* / Q000187:drug effects; D012717:Sesquiterpenes / Q000494:pharmacology*; D013057:Spectrum Analysis; D013550:Swimming; D013997:Time Factors; D014131:Trace Elements / Q000494:pharmacology
D002121:Calcium Channel Blockers; D012717:Sesquiterpenes; D014131:Trace Elements; C493253:euplotin C; D002104:Cadmium; D009532:Nickel