Membrane permeability of coelenterazine analogues measured with fish eggs

To determine the suitability of various coelenterazine analogues for the regeneration of aequorin in living cells, the membrane permeabilities of 11 analogues were measured using the eggs of the killifish Fundulus grandis by soaking the eggs in solutions containing the analogues. The results indicated that e-coelenterazine, which has an exceptionally high rate of in vitro regeneration of aequorin, not only permeated poorly into the eggs but also was highly unstable. All other analogues tested permeated sufficiently into the eggs. The highest permeability was found with f-coelenterazine; the concentration of f-coelenterazine in the eggs was about five times that in the surrounding medium, assuming that the distribution of the compound in the egg is uniform.