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Co‐ordinated modulation of Ca2+ and K+ currents during ascidian muscle development.
Author(s) -
Greaves A A,
Davis A K,
Dallman J E,
Moody W J
Publication year - 1996
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.1996.sp021748
Subject(s) - chemistry , cardiac transient outward potassium current , biophysics , electrophysiology , resting potential , endocrinology , medicine , membrane potential , anatomy , patch clamp , neuroscience , biology
1. The development of Ca2+ and K+ currents was studied in ascidian muscle cells at twelve embryonic stages from gastrulation to the mature cell, a period of 24 h. A high degree of co‐ordination occurs between the development of the inwardly rectifying K+ current (IK(IR)), which sets the resting potential, and Ca2+ and outward K+ currents, which determine action potential waveform. 2. At neurulation IK(IR), which had been present since fertilization, begins to decrease, reaching 12% of its previous density in 6 h. IK(IR) then immediately begins to increase again, reaching its previous density in another 6 h. 3. When IK(IR) begins to decrease, a high‐threshold inactivating Ca2+ current and a slowly activating voltage‐gated K+ current appear. 4. When IK(IR) returns to its previous density, two new currents appear: a sustained Ca2+ current with the same voltage dependence, but different conotoxin sensitivity than the inactivating Ca2+ current; and a Ca(2+)‐dependent K+ current, which activates 8‐10 times faster and at potentials 20‐30 mV more negative than the voltage‐dependent K+ current. 5. The transient downregulation of IK(IR) destabilizes the resting potential and causes spontaneous action potentials to occur. Because IK(IR) is absent when only a slowly activating high‐threshold outward K+ current is present, these action potentials are long in duration. 6. The return of IK(IR) and the appearance of the rapidly activating Ca(2+)‐dependent K+ current eventually terminate this activity. The action potentials of the mature cell occur only on stimulation, and are 10 times shorter in duration than those in the immature cell.