An Anticalmodulin Drug, W-7, Inhibits the Voltage-Dependent Calcium Current in Paramecium Caudatum

The anticalmodulin drug, W-7 [N--(6 aminohexyl)-5-chloro-l-naph-thalenesulphonamide] specifically inhibits the voltage-dependent Ca-current of Paramecium as well as the behavioural consequence of Ca²⁺ influx, backward swimming. The dechlorinated analogue, W-5, is four to five times less effective. Analysis of membrane currents under voltage clamp shows that W-7 not only reversibly inhibits the voltage-dependent Ca-current but also shifts the voltage sensitivity of this Ca-current towards less negative voltages in a concentration-dependent manner. We suggest that Paramecium can be used as a system to screen behaviourally for other Ca-channel blockers as well as to study the mechanism of action of these drugs.