The ultimate objective of this research is to obtain insight into the mechanisms concerned in the activation of the egg during fertilization. Emphasis will be on investigating how membrane potential changes as signals are transduced into intracellular processes following sperm attachment. Electrophysiological measurements on voltage clamped eggs will be combined with video digital image processing to correlate electrical events with (a) morphological changes in the living cell difficult otherwise to resolve, (b) the occurrence of cortical actin filament assembly using fluorescently labeled actin or phallicidin, and (c) changes in intracellular ?Ca2+! and pH and the localization of these changes using fluorescent indicators and image ratioing methods. Investigation of the mechanism whereby membrane potentials in the neighborhood of resting (-70mV) suppress sperm entry (although activation proceeds) will be pursued. The possibility that the suppression of sperm entry is the consequence of an effect of negative membrane potential on assembly of actin filaments will be investigated. Dr. Chambers's laboratory has been active for many years in the study of the physiology of sea urchin egg activation at fertilization. The sea urchin egg is chosen in these studies because this egg (which has about the same size and yolk content as the human egg) is transparent, large, readily available in large numbers and withstands laboratory manipulations. In a more general context, the research is directed toward understanding the mechanisms whereby a quiescent cell, at rest, is activated to undergo mitosis, cell division and growth.
