Regulation of the transient outward K+ current by Ca2+/calmodulin-dependent protein kinases II in human atrial myocytes

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Item Type:	Article
Title:	Regulation of the transient outward K+ current by Ca2+/calmodulin-dependent protein kinases II in human atrial myocytes
Creators Name:	Tessier, S., Karczewski, P., Krause, E.G., Pansard, Y., Acar, C., Lang-Lazdunski, M., Mercadier, J.J. and Hatem, S.N.
Abstract:	Ca(2+)/calmodulin-dependent protein kinases II (CaMKII) have important functions in regulating cardiac excitability and contractility. In the present study, we examined whether CaMKII regulated the transient outward K(+) current (I(to)) in whole-cell patch-clamped human atrial myocytes. We found that a specific CaMKII inhibitor, KN-93 (20 micromol/L), but not its inactive analog, KN-92, accelerated the inactivation of I(to) (tau(fast): 66.9+/-4.4 versus 43.0+/-4.4 ms, n=35; P<0.0001) and inhibited its maintained component (at +60 mV, 4.9+/-0.4 versus 2.8+/-0.4 pA/pF, n = 35; P<0. 0001), leading to an increase in the extent of its inactivation. Similar effects were observed by dialyzing cells with a peptide corresponding to CaMKII residues 281 to 309 or with autocamtide-2-related inhibitory peptide and by external application of the calmodulin inhibitor calmidazolium, which also suppressed the effects of KN-93. Furthermore, the phosphatase inhibitor okadaic acid (500 nmol/L) slowed I(to) inactivation, increased I(sus), and inhibited the effects of KN-93. Changes in [Ca(2+)](i) by dialyzing cells with approximately 30 nmol/L Ca(2+) or by using the fast Ca(2+) buffer BAPTA had opposite effects on I(to). In BAPTA-loaded myocytes, I(to) was less sensitive to KN-93. In myocytes from patients in chronic atrial fibrillation, characterized by a prominent I(sus), KN-93 still increased the extent of inactivation of I(to). Western blot analysis of atrial samples showed that delta-CaMKII expression was enhanced during chronic atrial fibrillation. In conclusion, CaMKII control the extent of inactivation of I(to) in human atrial myocytes, a process that could contribute to I(to) alterations observed during chronic atrial fibrillation.
Keywords:	KN-93, K+ Channel, delta-CaMKII, Atrial Fibrillation, Heart
Source:	Circulation Research
ISSN:	0009-7330
Publisher:	American Heart Association
Volume:	85
Number:	9
Page Range:	810-819
Date:	29 October 1999
Official Publication:	http://circres.ahajournals.org/cgi/content/abstract/85/9/810
PubMed:	View item in PubMed

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