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Periodic increase of cytoplasmic free calcium in fertilized hamster eggs measured with calcium‐sensitive electrodes.
Author(s) -
Igusa Y,
Miyazaki S
Publication year - 1986
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1986.sp016181
Subject(s) - hamster , calcium , biophysics , cytoplasm , conductance , voltage clamp , chemistry , human fertilization , analytical chemistry (journal) , biology , membrane potential , endocrinology , anatomy , biochemistry , chromatography , physics , organic chemistry , condensed matter physics
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.