Electrical perception of the 'death message' in Chara: analysis of K+-sensitive depolarization

Wounding electrical responses were studied in Chara corallina. Specimens comprising two adjoining internodal cells were prepared. When one cell (victim cell) was cut, the other cell (receptor cell) generated four kinds of depolarization: (i) rapid depolarization; (ii) long-lasting depolarization; (iii) action potentials; and (iv) small spikes. In the present study, attention was focused on the long-lasting depolarization. A decrease in the electrical resistance suggested activation of ion channel(s). The duration of the depolarization was sensitive to the external ions. K(+) significantly prolonged the depolarization. On the other hand, Ca(2+), Mg(2+) and Na(+) had a tendency to shorten the duration prolonged by K(+). When a nodal end was continuously flushed with a medium lacking K(+), the depolarization was significantly shortened. Treatment of the nodal end with artificial cell sap for 2 min induced a long-lasting depolarization similar to that induced by cutting the victim cell. These findings suggested the involvement of K(+) released from the victim cell in generating the long-lasting depolarization by the receptor cell.