RESPONSES OF THE MEDAKA FISH EGG (ORYZIAS-LATIPES) TO THE PHOTOLYSIS OF MICROINJECTED NITROPHENYL-EGTA, A PHOTOLABILE CALCIUM CHELATOR

Photolabile calcium chelators (calcium cages) can be used to elevate c ytosolic [Ca2+] at specific sites and times (1, 2, 3). They have been especially valuable in flash photolysis studies of muscle contraction (2) and secretion (4, 5). In the present report, I describe several re sponses of medaka eggs to the photolysis of microinjected nitrophenyl- EGTA (NP-EGTA), a new calcium cage (6). When unfertilized eggs injecte d with NP-EGTA were irradiated with ultraviolet irradiation in a small region of the egg, the eggs were activated and ooplasm within the irr adiated region contracted and accumulated there. Eggs into which NP-EG TA was injected could also be fertilized. Subsequent irradiation of su ch eggs, in addition to causing the contraction and accumulation of oo plasm, also caused a global contraction of dividing blastomeres and th e contraction and blebbing of embryonic cells for up to 4 days after f ertilization. Injection of NP-EGTA had no apparent effect on the matur ation of fertilized eggs, which developed normally and hatched.