Effect of Cytochalasin B on the Development of Membrane Transports in Sea Urchin Eggs after Fertilization

Investigations were made on the role of the cytoskeleton in the onset of ionic events following fertilization of sea urchin eggs. Events which depend upon phosphoinositide metabolism, such as the cortical reantion and acid release are affected by cytochalasin B (CB) after fertilization but not after activation of eggs with the ionophore A23187. These findings suggest that the sequence of events following sperm-egg attachment depends on the cytoskeleton. CB also inhibits the Na⁺ pump and alanine uptake when added before insemination and during the following 30 min. These results argue for a role of the egg cortex cytoskeleton in activation of the Na⁺ pump by fertilization. We propose that the inhibitory effect of CB on the development of amino-acid uptake after fertilization may result from an increase in the Na⁺ content of the egg resulting from Na⁺ pump suppression rather than from direct blockage of the carrier.