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Developmental changes in delayed rectifier K+ currents in the muscular‐ and neural‐type blastomere of ascidian embryos.
Author(s) -
Shidara M,
Okamura Y
Publication year - 1991
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.1991.sp018834
Subject(s) - blastomere , chemistry , reversal potential , embryo , electrophysiology , cleavage (geology) , biophysics , patch clamp , anatomy , embryogenesis , biology , medicine , genetics , paleontology , fracture (geology)
1. Developmental changes in the amplitude, kinetic properties, tetraethyl‐ammonium (TEA) sensitivity, and ion selectivity of the delayed rectifier K+ currents were investigated in differentiating muscular‐type (M) and neural‐type (N) blastomeres isolated from the early cleavage‐arrested ascidian embryos, using conventional two‐microelectrode voltage clamp techniques. 2. No voltage‐sensitive outward K+ currents were found in either type of blastomere during the first 35 h of development at 9 degrees C. Thereafter the delayed rectifier K+ current became apparent. The peak amplitude of the K+ current in the M‐blastomere increased abruptly from 50 to 60 h and tended to plateau after 60 h, while in the N‐blastomere it continued to increase after initial emergence at around 35 h. 3. The threshold potential level of the K+ current in the M‐blastomere was initially about ‐10 mV in a standard external solution (1 mM‐K+ solution), but shifted towards the hyperpolarized direction until it reached a steady level at 45 h after fertilization. At the fully differentiated stages, the threshold was around ‐32 mV and ‐26 mV in the M‐ and N‐blastomeres, respectively. 4. Throughout development, the reversal potential of the tail current changed with the external K+ concentration in both M‐ and N‐blastomeres as expected for a K(+)‐electrode. There was no significant difference in the selectivity ratios for the K+ channel between the two types of blastomeres. The relative selectivities were K+ (1.000): Rb+ (0.774): NH4+ (0.122): Na+ (0.074) and K+ (1.000): Rb+ (0.724): NH4+ (0.155): Na+ (0.074) in the M‐ and N‐blastomeres, respectively. 5. Modified Scatchard plots of TEA‐sensitivity data indicated a one‐to‐one reaction between TEA and the K+ channel. These plots revealed the presence of TEA‐resistant K+ channels in addition to TEA‐sensitive K+ channels in the M‐blastomere, but revealed only TEA‐sensitive K+ channels in the N‐blastomere. The dissociation constant (Ki) values of these three types of K+ channel did not change during development. In the M‐blastomere, the Ki of the TEA‐sensitive K+ channel was 1.29 +/‐ 0.05 mM (mean +/‐ S.E.M., n = 31) and that of the TEA‐resistant K+ channel was 1.4 +/‐ 0.1 M (mean +/‐ S.E.M., n = 31) at a test potential of 45 mV. The Ki value of the neural‐type K+ current was 1.38 +/‐ 0.03 mM (mean +/‐ S.E.M., n = 20) at 45 mV.(ABSTRACT TRUNCATED AT 400 WORDS)