ISSN:
1432-2013
Keywords:
Cardiac myocytes
;
ATP-sensitive K+ current
;
K+ accumulation
;
Nicorandil
;
T-tubules
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract The mechanism of nicorandil-induced large inward tail current (I tail) in single guinea-pig ventricular cells was investigated using the whole-cell patch-clamp technique. In the presence of 0.5–1.0 mM nicorandil, an activator of adenosine 5′-triphosphate (ATP)-sensitive K+ current (I KATP), a depolarization pulse causing a large outward current was followed by a large inward I tail on the repolarization step to the holding potential at-85 mV. The larger the outward current, the greater the I tail. The amplitude of I tail increased as a single exponential function (τ=74.9 ms) as the duration of preceding depolarization was prolonged. Both the outward current and I tail were inhibited nearly completely after application of glibenclamide (1 μM), a specific blocker of I KATP. Substitution of K+ with Cs+ in both the external and internal solutions resulted in a virtual elimination of I tail. I tail was well preserved under the condition where Ca2+ entry during the preceding depolarization was largely inhibited or where external Na+ was replaced by Li+. A transient positive shift of reversal potential for the net current was observed at the peak of I tail. At 30 mM external K+ concentration, I tail was almost eliminated. From these findings, it is concluded that the I tail is a K+ current associated with an alteration of the K+ equilibrium potential (E K) following a substantial K+ efflux. This E K change is most likely explained by an accumulation of K+in transverse tubules (T-tubules) since I tail was not induced in atrial cells in which T-tubules are poorly developed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00374293
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