Electrophysiology of the marine diatom Coscinodiscus wailesii -: I.: Endogenous changes of membrane voltage and resistance

Double-barrelled micropipettes have been used to record the endogenous electrical behaviour of the marine diatom Coscinodiscus wailesii, diameter about 250 mu m, surface area about 0.2 mm(2). The conclusion is that the membrane is not in a genuine steady-state but rather the membrane changes spontaneously between several characteristic modes, There are periods of pseudo-steady-state in which the membrane voltage is rather stable in the range between -60 and -90 mV over about 1 h, and stable resistances can be found between 0.1 and 1.0 M Ohm. Dynamic stages are also characteristic: various types of oscillations (sinusoidal, saw-tooth and complex non-linear) with parallel and antiparallel phase relations between voltage and resistance, as well as transient voltage excursions down to -165 mV, revealing the operation of an electrogenic pump. The observed phenomena may be interpreted in terms of an electrical equivalent circuit with three parallel limbs: an electrogenic pump with a linear conductance, a K+ pathway with saturating currents of about -400 and +50 nA, and a linear Cl- conductance, each with a stable electromotive force and a variable proportion of activity.