Sinoatrial node pacemaker activity requires Ca2+/calmodulin-dependent protein kinase II activation

Citation
Tm. Vinogradova et al., Sinoatrial node pacemaker activity requires Ca2+/calmodulin-dependent protein kinase II activation, CIRCUL RES, 87(9), 2000, pp. 760-767
Citations number
33
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Cardiovascular & Hematology Research
Journal title
CIRCULATION RESEARCH
ISSN journal
0009-7330 → ACNP
Volume
87
Issue
9
Year of publication
2000
Pages
760 - 767
Database
ISI
SICI code
0009-7330(20001027)87:9<760:SNPARC>2.0.ZU;2-W
Abstract
Cardiac beating arises from the spontaneous rhythmic excitation of sinoatri al (SA) node cells. Here we report that SA node pacemaker activity is criti cally dependent on Ca2+/calmodulin-dependent protein kinase II (CaMKII). In freshly dissociated rabbit single SA node cells, inhibition of CaMKII by a specific peptide inhibitor, autocamtide-2 inhibitory peptide (AIP, 10 mu m ol/L), or by KN-93 (0.1 to 3.0 mu mol/L), but not its inactive analog, KN-9 2, depressed the rate and amplitude of spontaneous action potentials (APs) in a dose-dependent manner. Strikingly, 10 mu mol/L AIP and 3 mu mol/L KN-9 3 completely arrested SA node cells, which indicates that basal CaMKII acti vation is obligatory to the genesis of pacemaker AP. To understand the ioni c mechanisms of the CaMKII: effects, we measured L-type Ca2+ current (I-Ca, I-L), which contributes both to AP upstroke and to pacemaker depolarization . KN-93 (1 mu mol/L), but not its inactive analog, KN-92, decreased I-Ca,I- L amplitude from 12+/-2 to 6+/-1 pA/pF without altering the shape of the cu rrent-voltage relationship. Both AIP and KN-93 shifted the midpoint of the steady-state inactivation curve leftward and markedly slowed the recovery o f I-Ca,I-L from inactivation. Similar results were observed using the fast Ca2+ chelator BAPTA, whereas the slow Ca2+ chelator EGTA had no significant effect, which suggests that CaMKII activity is preferentially regulated by local Ca2+ transients. Indeed, confocal immunocytochemical imaging showed that active CaMKII is highly localized beneath the surface membrane in the vicinity of L-type channels and that ATP and KN-93 significantly reduced Ca MKII activity. Thus, we conclude that CaMKII plays a vital role in regulati ng cardiac pacemaker activity mainly via modulating I-Ca,I-L inactivation a nd reactivation, and local Ca2+ is critically involved in these processes.