Electrical coupling and release of K+ from endothelial cells co-mediate ACh-induced smooth muscle hyperpolarization in guinea-pig inner ear artery.
The physiological basis of ACh-elicited hyperpolarization in guinea-pig in vitro cochlear spiral modiolar artery (SMA) was investigated by intracellular recording combined with dye labelling of recorded cells and immunocytochemistry. We found the following. (1) The ACh-hyperpolarization was prominent only in cells that had a low resting potential (less negative than -60 mV). ACh-hyperpolarization was reversibly blocked by 4-DAMP, charybdotoxin or BAPTA-AM, but not by N(omega)-nitro-L-arginine methyl ester, glipizide, indomethacin or 17-octadecynoic acid. (2) Ba(2)(+) (100 microm) and ouabain (1 microm) each attenuated ACh-hyperpolarization by approximately 30% in smooth muscle cells (SMCs) but had only slight or no inhibition in endothelial cells (ECs). A combination of Ba(2)(+) and 18beta-glycyrrhetinic acid near completely blocked the ACh-hyperpolarization in SMCs. (3) High K(+) (10 mm) induced a smaller hyperpolarization in ECs than in SMCs, with an amplitude ratio of 0.49 : 1. Ba(2)(+) blocked the K(+)-induced hyperpolarization by approximately 85% in both cell types, whereas ouabain inhibited K(+)-hyperpolarization differently in SMCs (19%) and ECs (35%) and increased input resistance. 18beta-Glycyrrhetinic acid blocked the high K(+)-hyperpolarization in ECs only. (4) Weak myoendothelial dye coupling was detected by confocal microscopy in cells recorded with a propidium iodide-containing electrode for longer than 30 min. A sparse plexus of choline acetyltransferase-immunoreactive (ChAT) fibres was observed around the SMA and its up-stream arteries. (5) Evoked excitatory junction potentials (EJP) were partially blocked by 4-DAMP in half of the cells tested. We conclude that ACh-induced hyperpolarization originates from ECs via activation of Ca(2)(+)-activated potassium channels, and is independent of the release of NO, cyclo-oxygenase or cytochrome P450 products. ACh-induced hyperpolarization in smooth muscle cells involves two mechanisms: (a) electrical spread of the hyperpolarization from the endothelium, and (b) activation of inward rectifier K(+) channels (K(ir)) and Na(+)-K(+) pump current by elevated interstitial K(+) released from the endothelial cells, these being responsible for about 60% and 40% of the hyperpolarization, respectively. The role ratio of K(ir) and pump current activation is at 8 : 1 or less.
Jiang
Zhi-Gen
ZG
Oregon Hearing Research Center, NRC04, Oregon Health & Science University, Portland, OR 97239, USA. jiangz@ohsu.edu
Nuttall
Alfred L
AL
Zhao
Hui
H
Dai
Chun-Fu
CF
Guan
Bing-Cai
BC
Si
Jun-Qiang
JQ
Yang
Yu-Qin
YQ
D000109:Acetylcholine / Q000494:pharmacology* / Q000502:physiology; D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000502:physiology; D003051:Cochlea / Q000098:blood supply* / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D007758:Ear, Inner / Q000098:blood supply / Q000187:drug effects / Q000502:physiology; D042783:Endothelial Cells / Q000187:drug effects / Q000502:physiology*; D006168:Guinea Pigs; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology
D024661:Potassium Channels, Inwardly Rectifying; D000254:Sodium-Potassium-Exchanging ATPase; D000109:Acetylcholine; D011188:Potassium
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