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Electrical coupling and release of K + from endothelial cells co‐mediate ACh‐induced smooth muscle hyperpolarization in guinea‐pig inner ear artery
Author(s) -
Jiang ZhiGen,
Nuttall Alfred L.,
Zhao Hui,
Dai ChunFu,
Guan BingCai,
Si JunQiang,
Yang YuQin
Publication year - 2005
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2004.080960
Subject(s) - hyperpolarization (physics) , ouabain , apamin , charybdotoxin , biophysics , membrane potential , cyclopiazonic acid , carbenoxolone , chemistry , medicine , biology , biochemistry , intracellular , potassium channel , gap junction , stereochemistry , organic chemistry , nuclear magnetic resonance spectroscopy , sodium
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 ω ‐nitro‐ l ‐arginine methyl ester, glipizide, indomethacin or 17‐octadecynoic acid. (2) Ba 2 + (100 μ m ) and ouabain (1 μ m ) each attenuated ACh‐hyperpolarization by ∼30% in smooth muscle cells (SMCs) but had only slight or no inhibition in endothelial cells (ECs). A combination of Ba 2 + and 18β‐glycyrrhetinic acid near completely blocked the ACh‐hyperpolarization in SMCs. (3) High K + (10 m m ) 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 ∼85% in both cell types, whereas ouabain inhibited K + ‐hyperpolarization differently in SMCs (19%) and ECs (35%) and increased input resistance. 18β‐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.