K+ channels and their effects on membrane potential in rat bronchial smooth muscle cells.
In order to investigate the K+ channels and their effects on resting membrane potential (Em) and excitability in rat bronchial smooth muscle cells (BSMCs), the components of outward K+ channel currents and the effects of K+ channels on Em and tension in rat bronchial smooth muscle were observed by using standard whole-cell recording of patch clamp and isometric tension recording techniques. The results showed that under resting conditions, total outward K+ channel currents in freshly isolated BSMCs were unaffected by ATP-sensitive K+ channel blocker. There were two types of K+ currents: voltage-dependent delayed rectifier K+ channel (Kv) and large conductance calcium-activated K+ channel (BKCa) currents. 1 mmol/L 4-aminopyridine (4-AP, an inhibitor of Kv) caused a significant depolarization (from -8.7 +/- 5.9 mV to -25.4 +/- 3.1 mV, n = 18, P < 0.001). In contrast, 1 mmol/L tetraethylammonium (TEA, an inhibitor of BKca) had no significant effect on Em (from -37.6 +/- 4.8 mV to -36.8 +/- 4.1 mV, n = 12, P > 0.05). 4-AP caused a concentration-dependent contraction in resting bronchial strips. TEA had no effect on resting tension, but application of 5 mmol/L TEA resulted in a left shift with bigger pD2 (the negative logarithm of the drug concentration causing 50% of maximal effect) (from 6.27 +/- 0.38 to 6.89 +/- 0.54, n = 10, P < 0.05) in the concentration-effect curve of endothine-1, and a right shift with smaller pD2 (from 8.10 +/- 0.23 to 7.69 +/- 0.08, n = 10, P < 0.05) in the concentration-effect curve of isoprenaline. It was suggested that in rat BSMCs there may be two types of K+ channels, Kv and BKca, which serve distinct roles. Kv participates in the control of resting Em and tension. BKca is involved in the regulation of relaxation or contraction associated with excitation.
Liu
Xiansheng
X
Department of Respiratory Medicine, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030.
Xu
Yongjian
Y
Zhang
Zhenxiang
Z
Ni
Wang
W
D000818:Animals; D001980:Bronchi / Q000378:metabolism* / Q000502:physiology*; D002478:Cells, Cultured; D008564:Membrane Potentials; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D024681:Potassium Channels, Calcium-Activated / Q000378:metabolism / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D024681:Potassium Channels, Calcium-Activated; D024642:Potassium Channels, Voltage-Gated