Characteristic of spontaneous transient outward potassium currents in vascular smooth muscle cells of porcine coronary artery.
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 mumol/L) respectively. In contrast, CdCl2 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 BK(Ca) 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.
Cai
Fang
F
Institute of Myocardial Electrophysiology, Luzhou Medical College, Luzhou 646000, China.
Li
Peng-Yun
PY
Yang
Yan
Y
Liu
Zhi-Fei
ZF
Li
Miao-Ling
ML
Zhou
Wen
W
Pei
Jie
J
Cheng
Jun
J
Lan
Huan
H
Grammer
Joachim B
JB
Zeng
Xiao-Rong
XR
D000818:Animals; D003331:Coronary Vessels / Q000166:cytology* / Q000502:physiology; D055724:Electrophysiological Phenomena / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000502:physiology; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000502:physiology*; D018408:Patch-Clamp Techniques; D024681:Potassium Channels, Calcium-Activated / Q000502:physiology*; D019831:Sodium-Calcium Exchanger / Q000502:physiology*; D013552:Swine
D024681:Potassium Channels, Calcium-Activated; D019831:Sodium-Calcium Exchanger