An electrophysiological study of regeneration in Acetabularia mediterranea.
Polar regeneration of anucleate posterior stalk segments (PSS) of Acetabularia mediterranea has been studied electrophysiologically. 1. During regeneration the PSS develops a longitudinal, steady potential gradient, U, which is shown to reflect a spatial difference in the transmembrane potential, ΔV m,of 5 to 10 mV, i.e. about 5% of V m.While regeneration becomes visible at about t r=45 h after its light-triggered onset, its sign can be predicted from U not later than at t=29 h, because regeneration occurs at that cell pole where V mis highest, i.e. where the cytoplasm is more negative (Fig. 3, Table 1). 2. Clamping U to comparable values by external circuitry causes the regeneration again to occur where V mis highest, although in this case the flow of the current, I, which controls U is opposite to the direction of the self-generated current, or even changes its sign (Fig. 11, Table 2). 3. Clamping U to zero, i.e. eliminating any transcellular potential gradient, inhibits polar regeneration at least up to t=60 h (Table 3). 4. Spontaneous spikes of U (Fig. 4) and of I (Fig. 12), occur as early as at t=8 h (Fig. 5). These spikes arise at the presumptive regenerating pole with refractory intervals of 10-25 min. They obviously reflect the propagating action potential (Figs. 7-9) although, under the conditions of our present experiments, they spread along the PSS only electrotonically (Fig. 6). 5. Both signals, U and the spikes, are presumably due to changes in the electrogenic Cl-dependent component of V m,rather than its K(+)-controlled, diffusive component. 6. The data allow to substantiate our working-hypothesis (p. 242) that the mechanism of spatial differentiation involves voltage-dependent plasmalemma properties including excitation.
Biophysical Laboratory, Institute of Biology, University of Tübingen, Germany.
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Novák
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Bentrup