Electrical and morphological responses of the lobster egg to fertilization

Abstract

The electrophysiological and morphological characteristics of fully grown immature and fertilizable mature oocytes of the European lobster Homarus gammarus are described. In fully grown immature oocytes with a centrally located germinal vesicle, the resting potential was −54 ± 1.5 mV ( n = 32) and the membrane was K + selective. Fully grown immature oocytes with a peripheral germinal vesicle whose E m was −40 ± 1.5 mV ( n = 11), were predominantly permeable to K +, and slightly permeable to Cl −. In mature oocytes arrested at first meiotic metaphase the plasma membrane was selectively permeable to Cl −, and E m was −32 ± 2 mV ( n = 16). Mature oocytes were inseminated in vitro with sperm from the thelycum or female sperm receptacle. Insemination instantaneously triggered a sustained hyperpolarization that corresponded to the fertilization potential, and was caused by increased membrane permeability to K +. Concomitant with this electrical response, the oocyte, which before insemination had been in first metaphase, resumed its meiotic maturation. One hour after insemination, the nucleus of the penetrating spermatozoon was in the egg cortex.