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Hyperpolarization of isolated capillaries from guinea‐pig heart induced by K + channel openers and glucose deprivation
Author(s) -
Langheinrich Ulrike,
Daut Jürgen
Publication year - 1997
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 - 10.1111/j.1469-7793.1997.397bk.x
Subject(s) - hyperpolarization (physics) , glibenclamide , membrane potential , diazoxide , chemistry , ionophore , pinacidil , biophysics , charybdotoxin , membrane , biochemistry , endocrinology , biology , stereochemistry , nuclear magnetic resonance spectroscopy , insulin , diabetes mellitus
1 The present study was designed to test if microvascular coronary endothelial cells express ATP–sensitive K + channels (K ATP channels). We performed microfluorometric measurements of the membrane potential of freshly isolated guinea‐pig coronary capillaries equilibrated with the voltage–sensitive dye bis‐oxonol (bis‐[1,3–dibutylbarbituric acid] trimethineoxonol, [DiBAC 4 (3)]). 2 The resting membrane potential of capillaries in physiological salt solution was −46±4.2 mV ( n = 8 ) at room temperature (22 °C) as determined after calibration of the fluorescence using the Na + –K + ionophore gramicidin in the presence of different K + concentrations. Spontaneous membrane potential fluctuations of 10–20 mV amplitude were often observed. 3 A reversible, sustained hyperpolarization to a new membrane potential close to the K + equilibrium potential ( E K ) could be induced by application of the K + channel openers HOE 234 (100 nm to 1 μ M ), diazoxide (10 pm to 100 n M ) or pinacidil (100 n M ). Subsequent addition of glibenclamide (200 nm to 2 μ M ) reversed this hyperpolarization. 4 A glibenclamide–sensitive hyperpolarization of coronary capillaries to values near E K was also observed upon omission of D ‐glucose (10 m M ) from the superfusing solution or by substituting L‐glucose for D ‐glucose. Maximum hyperpolarization was reached in less than 10 min. 5 Our results suggest that microvascular coronary endothelial cells express K ATP channels which may be activated during hypoglycaemia.