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.
Center for Brain Science Research, Department of Physiology and Biophysics, School of Life Sciences, Fudan University, Shanghai, China.
MiOu
M
Zhou
Zheng
Z
Liu
ChangLong
C
Hu
ZhiHong
Z
Zhang
YanAi
Y
Mei
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