An electrophysiological study of regeneration in Acetabularia mediterranea

Summary

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.