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Pharmacological block of the slow component of the outward delayed rectifier current ( I Ks ) fails to lengthen rabbit ventricular muscle QT c and action potential duration

Pharmacological block of the slow component of the outward delayed rectifier current ( I Ks )... The effects of IKs block by chromanol 293B and L‐735,821 on rabbit QT‐interval, action potential duration (APD), and membrane current were compared to those of E‐4031, a recognized IKr blocker. Measurements were made in rabbit Langendorff‐perfused whole hearts, isolated papillary muscle, and single isolated ventricular myocytes. Neither chromanol 293B (10 μM) nor L‐735,821 (100 nM) had a significant effect on QTc interval in Langendorff‐perfused hearts. E‐4031 (100 nM), on the other hand, significantly increased QTc interval (35.6±3.9%, n=8, P<0.05). Similarly both chromanol 293B (10 μM) and L‐735,821 (100 nM) produced little increase in papillary muscle APD (less than 7%) while pacing at cycle lengths between 300 and 5000 ms. In contrast, E‐4031 (100 nM) markedly increased (30 – 60%) APD in a reverse frequency‐dependent manner. In ventricular myocytes, the same concentrations of chromanol 293B (10 μM), L‐735,821 (100 nM) and E‐4031 (1 μM) markedly or totally blocked IKs and IKr, respectively. IKs tail currents activated slowly (at +30 mV, τ=888.1±48.2 ms, n=21) and deactivated rapidly (at −40 mV, τ=157.1±4.7 ms, n=22), while IKr tail currents activated rapidly (at +30 mV, τ=35.5±3.1 ms, n=26) and deactivated slowly (at −40 mV, τ1=641.5±29.0 ms, τ2=6531±343, n=35). IKr was estimated to contribute substantially more to total current density during normal ventricular muscle action potentials (i.e., after a 150 ms square pulse to +30 mV) than does IKs. These findings indicate that block of IKs is not likely to provide antiarrhythmic benefit by lengthening normal ventricular muscle QTc, APD, and refractoriness over a wide range of frequencies. British Journal of Pharmacology (2001) 132, 101–110; doi:10.1038/sj.bjp.0703777 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png British Journal of Pharmacology Wiley

Pharmacological block of the slow component of the outward delayed rectifier current ( I Ks ) fails to lengthen rabbit ventricular muscle QT c and action potential duration

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References (58)

Publisher
Wiley
Copyright
2001 British Pharmacological Society
ISSN
0007-1188
eISSN
1476-5381
DOI
10.1038/sj.bjp.0703777
pmid
11156566
Publisher site
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Abstract

The effects of IKs block by chromanol 293B and L‐735,821 on rabbit QT‐interval, action potential duration (APD), and membrane current were compared to those of E‐4031, a recognized IKr blocker. Measurements were made in rabbit Langendorff‐perfused whole hearts, isolated papillary muscle, and single isolated ventricular myocytes. Neither chromanol 293B (10 μM) nor L‐735,821 (100 nM) had a significant effect on QTc interval in Langendorff‐perfused hearts. E‐4031 (100 nM), on the other hand, significantly increased QTc interval (35.6±3.9%, n=8, P<0.05). Similarly both chromanol 293B (10 μM) and L‐735,821 (100 nM) produced little increase in papillary muscle APD (less than 7%) while pacing at cycle lengths between 300 and 5000 ms. In contrast, E‐4031 (100 nM) markedly increased (30 – 60%) APD in a reverse frequency‐dependent manner. In ventricular myocytes, the same concentrations of chromanol 293B (10 μM), L‐735,821 (100 nM) and E‐4031 (1 μM) markedly or totally blocked IKs and IKr, respectively. IKs tail currents activated slowly (at +30 mV, τ=888.1±48.2 ms, n=21) and deactivated rapidly (at −40 mV, τ=157.1±4.7 ms, n=22), while IKr tail currents activated rapidly (at +30 mV, τ=35.5±3.1 ms, n=26) and deactivated slowly (at −40 mV, τ1=641.5±29.0 ms, τ2=6531±343, n=35). IKr was estimated to contribute substantially more to total current density during normal ventricular muscle action potentials (i.e., after a 150 ms square pulse to +30 mV) than does IKs. These findings indicate that block of IKs is not likely to provide antiarrhythmic benefit by lengthening normal ventricular muscle QTc, APD, and refractoriness over a wide range of frequencies. British Journal of Pharmacology (2001) 132, 101–110; doi:10.1038/sj.bjp.0703777

Journal

British Journal of Pharmacology – Wiley

Published: Jan 1, 2001

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