Spontaneous and induced changes in the membrane potential and resistance ofAcetabularia mediterranea

Abstract

The normal resting potential across theAcetabularia mediterranea cell membrane is -170 mV and the resistance is about 0.1 kΩ·cm(2). The time courses of potential and resistance changes have been studied in connection with several slow dynamic properties of the membrane. These effects include spontaneous and stimulated depolarizing spikes, spontaneous repolarization after prolonged maintenance of a quasistable depolarized condition, and a hyperpolarizing response when current is applied to the cell in this depolarized state. These processes show considerable similarities to each other, which suggests that they might all be explained by changes in permeability to Cl(-). In normal conditions, membrane punch-through occurs with a relatively small hyperpolarizing bias.

“Metabolic” action potentials inAcetabularia

“…If the intensity of the light is increased again by the factor 10, the on-effect is again faster and larger; however, the off-effect is qualitatively completely different. First, the depolarization slows down normally during the first seconds, but then it speeds up again to a rapid and large depolarization below the equilibrium potential of potassium E~ of about -90 mV 1-2, 3,16]. From there on the depolarization is retarded again until it reaches the peak before repolarization.…”

“…Since photosynthetically active light raises the resting potential of Acetabularia [16], it seems to be possible that the light has also an effect on the action potential via the energy metabolism. In fact, it has been shown that the action currents under voltage clamp conditions strongly increase with the dose of the preceding light pulse [2].…”

Analog circuit of theAcetabularia membrane

“…The former current-voltage data of Gradmann [11] were only input measurements, neglecting the cable properties. Saddler's [27] data of the membrane resistance are also of limited significance, since the techniques and analysis of these experiments, worked out for Nitella [18], do not apply for Acetabularia where the length constant can be much shorter than the length of the cell. In order to incorporate the electrical properties in the total picture of the membrane, quantitative data are necessary.…”