K⁺ channels and their effects on membrane potential in rat bronchial smooth muscle cells

Abstract

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 (K_v) and large conductance calcium-activated K⁺ channel (BK_Ca) currents. 1 mmol/L 4-aminopyridine (4-AP, an, inhibitor of K_V) 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 BK_Ca) 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, K_v and BK_Ca, which serve distinct roles. K_v participates in the control of resting Em and tension. BK_Ca is involved in the regulation of relaxation or contraction associated with excitation.

Keywords

airway smooth muscle cells / K⁺ channel / membrane potential

References

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