The rise and fall of intracellular pH of sea urchin eggs after fertilisation

Abstract

JOHNSON et al.¹ have reported an increase in the intracellular pH of sea urchin eggs, seen between 1 and 4 min after insemination, that results from the efflux of H⁺ ions from the cells. The rise in pH can be induced by artificial activators of metabolism such as ammonia, or organic amines such as procaine. They have postulated that this increase in cellular pH is responsible for the metabolic derepression of the eggs and the initiation of embryonic development^1,2. Our interest in the control of the initiation of DNA synthesis in these synchronously dividing cells³, coupled with their method¹ for estimating the intracellular pH, led us to attempt to determine if fluctuations in pH occur during the cell cycle. Here we confirm the important observation of a rise in pH at fertilisation, and we report that the rise is soon followed by a gradual drop in pH to final values lower than those of the unfertilised condition.