Periodic increase of cytoplasmic free calcium in fertilized hamster eggs measured with calcium‐sensitive electrodes.

Open Access
Publisher Website
Google Scholar
Abstract
The hamster egg at fertilization shows transient, periodic hyperpolarizing responses due to a Ca2+‐activated K+ conductance. The suggested increase of the intracellular Ca2+ concentration ([Ca2+]i) was measured with Ca2+‐sensitive microelectrodes in combination with the voltage‐clamp technique. Calculated values of the basal [Ca2+]i before fertilization averaged in the range 0.2‐0.4 microM. Insemination of eggs induced periodic Ca2+ transients with exact one‐to‐one correspondence to periodic, Ca2+‐activated K+ currents. They were recorded anywhere in the cytoplasm, even far from the site of sperm‐egg fusion, indicating that [Ca2+]i increases in the whole egg upon each response. During a series of responses after insemination the increase in [Ca2+]i reached 1‐2 microM in the first three responses and the peak value decreased to 0.7‐0.8 microM in the later responses. The rise and decay times of each Ca2+ transient were 6.8 +/‐ 2.8 and 22 +/‐ 6 s (mean +/‐ S.D., n = 36), respectively. No significant difference in the amplitude and time course of the Ca2+ transient was detected in relation to the depth of the cytoplasm about 3‐30 micron from the surface. The basal [Ca2+]i increased gradually from 0.39 to 0.56 microM (average in fourteen eggs) during the series of Ca2+ transients. The biological significance and mechanism of the periodic increase in [Ca2+]i and the response time of the Ca2+ electrode are discussed.