Wound healing in jellyfish striated muscle involves rapid switching between two modes of cell motility and a change in the source of regulatory calcium

Small wounds (1.2 mm in diameter) made in the sheet of myoepithelial cells forming the "swimmintg" muscle of the jellyfish, Polyorchis penicillatus, w ere closed within 10 h by epithelial cells migrating centripetally to the w ound center. Some 24 to 48 h later these cells redifferentiated into fully contractile muscle cells. Labeling with bromodeoxyuridine failed to reveal any cell proliferation during this process. Phenotype switching (within 1 h ) from contractile muscle cells to migratory cells did not require synthesi s of new protein as shown by treatment with 40 mu M cycloheximide. Excitati on-contraction coupling in undamaged muscle depended on entry of Ca2+ throu gh voltage-gated ion channels, as shown by a block of contractility by 40 m u M nitrendipine and also on calcium released from intracellular stores sin ce caffeine (10 mM) caused a 25% reduction in contractile force. In contras t, migratory cells did not require a source of extracellular calcium since migration was unimpeded by low (1 mu M) free Ca2+ or nitrendipine. Instead, modulatory calcium was derived from intracellular stores since caffeine (1 0 mM) and thapsigargin (10 mu M) slowed migration. This lack of dependence on calcium influx in migratory cells was further confirmed by a dramatic do wn-regulation in voltage-gated inward current as shown by whole-cell patch recordings. (C) 2000 Academic Press.