Co-ordinated modulation of Ca2+ and K+ currents during ascidian muscle development

Adrienne A. Greaves, Anna K. Davis, Julia E. Dallman, William J. Moody

Research output: Contribution to journalArticle

25 Scopus citations

Abstract

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 (I(K(IR))), which sets the resting potential, and Ca2+ and outward K+ currents, which determine action potential, waveform. 2. At neurulation I(K(IR)), which had been present since fertilization, begins to decrease, reaching 12% of its previous density in 6 h. I(K(IR)) then immediately begins to increase again, reaching its previous density in another 6 h. 3. When I(K(IR)) begins to decrease, a high-threshold inactivating Ca2+ current and a slowly activating voltage-gated K+ current appear. 4. When I(K(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 Ca2+-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 I(K(IR)) destabilizes the resting potential and causes spontaneous action potentials to occur. Because I(K(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 I(K(IR)) and the appearance of the rapidly activating Ca2+-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.

Original languageEnglish (US)
Pages (from-to)39-52
Number of pages14
JournalJournal of Physiology
Volume497
Issue number1
DOIs
StatePublished - Nov 15 1996

ASJC Scopus subject areas

  • Physiology

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