PT  - JOURNAL ARTICLE
AU  - AK Davis
AU  - AA Greaves
AU  - JE Dallman
AU  - WJ Moody
TI  - Comparison of ionic currents expressed in immature and mature muscle cells of an ascidian larva
AID  - 10.1523/JNEUROSCI.15-07-04875.1995
DP  - 1995 Jul 01
TA  - The Journal of Neuroscience
PG  - 4875--4884
VI  - 15
IP  - 7
4099  - http://www.jneurosci.org/content/15/7/4875.short
4100  - http://www.jneurosci.org/content/15/7/4875.full
SO  - J. Neurosci.1995 Jul 01; 15
AB  - We have compared the voltage-gated ion channels present in larval ascidian muscle at two developmental stages: muscle precursor cells just after the terminal cell division and mature contractile muscle, 7- 11 hr later. All precursor cells express a high-threshold transient Ca current and a slowly activating delayed K current, and about half the cells express a low-threshold transient Ca current. An inwardly rectifying K current, which had been present from fertilization until just before the terminal cell division, is absent. Mature muscle retains two of the tailbud currents: the low-threshold transient Ca current and the slow delayed K current, although at larger densities, and also expresses a high-threshold Ca current that is similar in most respects to the precursor cell current but that lacks inactivation. In addition, mature muscle expresses two rapidly activating outward K currents, one voltage and one Ca dependent, that generate a composite outward K current that is eight times larger and activates eight times faster than the tailbud K current. Mature muscle also reexpresses the inward rectifier. We propose that the transient absence of the inward rectifier and the slow activation of the delayed K current early in development create a window of developmental time when spontaneous electrical activity is likely.