In:
American Journal of Physiology-Heart and Circulatory Physiology, American Physiological Society, Vol. 291, No. 1 ( 2006-07), p. H29-H37
Kurzfassung:
A long QT mutation in the cardiac sodium channel, D1790G (DG), shows enhanced flecainide use-dependent block (UDB). The relative importance of open and inactivated states of the channel in flecainide UDB has been controversial. We used a modifiable, inactivation-deficient mutant channel that contains the F1486C mutation in the IFM motif to investigate the UDB difference between the wild-type (WT-ICM) and DG (DG-ICM) channels. UDB at 5 Hz was greater in DG-ICM than WT-ICM, and IC 50 values for steady-state UDB were 7.19 and 18.06 μM, respectively. When [2-(trimethyammonium) ethyl]methanethiosulfonate bromide (MTSET) was included in the pipette and fast inactivation was disabled, IC 50 was 5.04 μM for DG-ICM and 12.63 μM for WT-ICM. We measured open-channel block by flecainide directly in MTSET-treated, noninactivating ICM channels. Steady-state block was higher for DG-ICM than WT-ICM (IC 50 was 2.34 μM for DG-ICM and 5.87 μM for WT-ICM), suggesting that open-channel block is an important determinant of flecainide UDB. We obtained association ( k on ) and dissociation ( k off ) rates for open-channel block by the Langmuir-isotherm model. They were k off = 31.37 s −1 , k on = 5.83 s −1 ·μM −1 , and calculated K d = 5.38 μM for WT-ICM (where K d = k off / k on ); and k off = 24.88 s −1 , k on = 9.54 s −1 ·μM −1 , and calculated K d = 2.61 μM for DG-ICM. These K d values were similar to IC 50 measured from steady-state open-channel block. Furthermore, we modeled UDB mathematically by using these kinetic rates and found that the model predicted experimental UDB accurately. The recovery from UDB had a minor contribution to UDB. Flecainide UDB is predominantly determined by an open-channel blocking mechanism, and DG-ICM channels appeared to have an altered open-channel state with higher flecainide affinity than WT-ICM.
Materialart:
Online-Ressource
ISSN:
0363-6135
,
1522-1539
DOI:
10.1152/ajpheart.01317.2005
Sprache:
Englisch
Verlag:
American Physiological Society
Publikationsdatum:
2006
ZDB Id:
1477308-9
SSG:
12
