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Characteristic of spontaneous transient outward potassium currents in vascular smooth muscle cells of porcine coronary artery

Cai Fang, Li Pengyun, Yang Yan, Liu Zhifei, Li Miaoling, Zhou Wen, Pei Jie, Cheng Jun, Lan Huan, Grammer J B, Zeng Xiaorong

Institute of Myocardial Electrophysiology, Luzhou Medical College.Luzhou 646000,Sichuan；Germany

Abstract

Spontaneous transient outward currents (STOCs) play an important role in the myogenic regulation of small artery tone,such as coronary artery. In the present study, we investigated the electrophysiological properties and the regulation of STOCs in vascular smooth muscle cells (VSMCs) of porcine coronary artery by perforated patch-clamp technique. Our data showed that STOCs were dependent on voltage and extracellular calcium and they were highly variable in amplitudes and frequencies. STOCs superimposed stochastically onto whole-cell K~(+) currents induced by step and ramp protocols. STOCs were completely abolished by ChTX [inhibitor of large-conductance Ca~(2+)-activated potassium (BK_(Ca)) channels], removal of extracellular Ca~(2+), or addition of ryanodine (50 #mu#mol/L) respectively. In contrast, CdCl_(2) and verapamil, inhibitors of voltage-dependent L-type Ca~(2+) channels, had little effect on STOCs.Caffeine (5 mmol/L) transiently increased STOCs (hump), followed by a temporary inhibition. Ca~(2+) ionophore A23187 increased both amplitude and frequency of STOCs. Na~(+) ionophore monensin increased the frequency of STOCs. STOCs were strongly inhibited by KB-R7943, a selective inhibitor of the reverse mode of the Na~(+)/Ca~(2+) exchanger. Based on these observations, we conclude that STOCs are mediated by BKCa channels. The generation and activation of STOCs depend upon Ca~(2+) influx through Na~(+)/Ca~(2+) exchange and release of Ca~(2+) from sarcoplasmic reticulum (SR) via ryanodine receptors. This suggests that Na~(+)/Ca~(2+) exchange determines calcium store refilling. Recycling of entering Ca~(2+) from superficial SR may locally elevate Ca~(2+) concentration at the plasma membrane, thereby activating BK_(Ca) channels and then initiating STOCs.

Key words: patch-clamp technique;smooth muscle;Potassium channel;sodium-calcium exchanger;ryanodine receptor

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Citing This Article：

Cai Fang, Li Pengyun, Yang Yan, Liu Zhifei, Li Miaoling, Zhou Wen, Pei Jie, Cheng Jun, Lan Huan, Grammer J B, Zeng Xiaorong. Characteristic of spontaneous transient outward potassium currents in vascular smooth muscle cells of porcine coronary artery. Acta Physiol Sin 2007; 59 (1): 27-34 (in Chinese with English abstract).