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Spontaneous activity regulates calcium‐dependent K + current expression in developing ascidian muscle
Author(s) -
Dallman Julia E.,
Davis Anna K.,
Moody William J.
Publication year - 1998
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 - 10.1111/j.1469-7793.1998.683bg.x
Subject(s) - chemistry , conductance , calcium , biophysics , electrophysiology , myocyte , medicine , endocrinology , biology , physics , organic chemistry , condensed matter physics
1 In embryonic ascidian muscle, outward K + currents develop in two stages: the initial expression of a slowly activating, voltage‐gated K + current ( I Kv ) near the time of neurulation is followed about 6 h later by a rapidly activating calcium‐activated K + current ( I K(Ca) ). During this 6 h interval, inward Ca 2+ currents ( I Ca ) appear and the inward rectifier ( I K(IR) ), the sole resting conductance, is transiently downregulated. These events predict a period of spontaneous activity. The following experiments were designed to test this prediction and to examine the relevance of spontaneous activity for muscle cell development. 2 By recording activity in cell‐attached patches, we have found that muscle cells generate spontaneous action potentials during this 6 h window of time when I K(IR) is downregulated and outward K + currents are slow. Action potentials occur at a mean frequency of 13.9 min −1 . 3 When activity is blocked by the transient application of the Ca 2+ channel blocker Cd 2+ , I K(Ca) fails to develop. This disruption is specific for I K(Ca) : I K(IR) and I Ca develop normally in activity‐blocked cells. Application of Cd 2+ either before or after the window of activity has no effect. 4 The reappearance of I K(IR) and the development of I K(Ca) and the mature form of I Ca are all prevented by transcription blockers, with a sensitive period corresponding to the period of activity. 5 These data show that, although the expression of three channel types depends on transcription during the period of spontaneous activity, only the development of I K(Ca) depends on activity.