Electrophysiology of the marine diatom Coscinodiscus wailesii IV: types ofnon-linear current-voltage-time relationships recorded with single saw-tooth voltage-clamp experiments

Electrophysiological states of the marine diatom Coscinodiscus wailesii are known to change spontaneously in the temporal range of seconds. In order t o assess the genuine current-voltage-time relationships of individual state s in less than a second, voltage-clamp experiments have been carried out us ing single sweeps of saw-tooth shaped command voltages. This method is intr oduced with model calculations. Plotting the results in current-voltage coo rdinates provides convenient access to several electrophysiological entitie s, such as absence of drift (smoothly closed IV loops), membrane capacitanc e (by I jump at sign reversal of dV/dt), and ohmic conductances tin linear regions of the current-voltage relationship), as well as equilibrium voltag e (internal intersection of capacitance-corrected, 8-shaped tracings) and c oarse gating kinetics (rise or fall of capacitance-corrected I at sign reve rsal of dV/dt) of a voltage-sensitive ion conductance. From electrophysiolo gical measurements with double-barreled glass-microelectrodes on C. wailesi i, several distinct types of current-voltage loops are presented. Most of t he data, including recordings from electrical excitation, can be interprete d as temporal relaxations of voltage-sensitive conductances for K+ and Cl-. A more detailed analysis of the effect of tetraethylammonium (TEA(+)) show s that 10 and 20 mM TEA(+) inhibit the K+ conductance in C. wailesii only b y up to about 20% but predominantly via a K+ outward rectifier.