Membrane potentials in excitable cells of aldrovanda vesiculosa trap-lobes

The resting membrane potential in excitable cells of Aldrovanda trap-lobes is composed of diffusion and electrogenic potentials. The diffusion potential, about -100 mV in artificial pond water, was determined from the external K⁺ and Na⁺ concentrations. The permeability ratio, P_Na/P_K of the membrane was estimated to be about 0.3. The electrogenic potential hyperpolarized the membrane to about -140 mV. The peak value of the action potential increased by +26 mV with a tenfold increase in the external Ca²⁺ concentration. The action potential was blocked by an application of the Ca²⁺ chelater or the Ca channel blocker, LaCl₃. Cells showed additional Ca²⁺ influx (7.8 pmole/cm² impulse) during membrane excitation. These facts suggest that the transient increase in Ca²⁺ influx causes the action potential present in cells of Aldrovanda trap-lobes.