Developmental regulation of a Na(+)-activated fast outward K+ current in rat myoblasts.
OBJECTIVE
Myoblasts undergoing differentiation sequentially express multiple K+ channels, and that ion channel expression varies depending on species and state of development. In this report, we reported a developmental regulation of fast activated and fast inactivated outward current in rat myoblasts.


METHODS
The kinetic and pharmacological property of the outward current was investigated by using the patch-clamp technique.


RESULTS
The outward current was elicited by a depolarizing step from -100 mV holding potential to +40 mV- +80 mV. The activation properties of this channel changed with days in culture. The outward current was blocked by 4-AP in a concentration dependent manner, with 0.5 mM and 2 mM 4-AP inhibiting the current by 10 +/- 3% and 56 +/- 3%, respectively. When 1 mM tetrodotoxin (TTX) was added to the bath solution or the membrane potential was depolarized to -50 mV, the fast outward current was aborted. Na+ dependent inhibition was observed when Na+ in the bath solution was replaced by Li+. In addition, replacement of K+ in the pipette solution by Cs+ almost completely eliminated the outward current.


CONCLUSIONS
The developmentally regulated outward current recorded in rat myoblasts is a Na+ influx-dependent outward K+ current, which may contribute to myoblast membrane firing of action potential or myoblast fusion.
Zhou
MiOu
M
Center for Brain Science Research, Department of Physiology and Biophysics, School of Life Sciences, Fudan University, Shanghai, China.
Liu
Zheng
Z
Hu
ChangLong
C
Zhang
ZhiHong
Z
Mei
YanAi
Y
D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002586:Cesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D024510:Muscle Development / Q000187:drug effects / Q000502:physiology*; D032448:Myoblasts, Skeletal / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology / Q000502:physiology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D012964:Sodium / Q000494:pharmacology / Q000502:physiology; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology
D015221:Potassium Channels; D015222:Sodium Channels; D002586:Cesium; D013779:Tetrodotoxin; D012964:Sodium; D011188:Potassium