kn-93 and Hypertension

Action potential duration alternans (APD-ALT), defined as long-short-long repetitive pattern of APD, potentially leads to lethal ventricular arrhythmia. However, the mechanisms of APD-ALT in the arrhythmogenesis of cardiac hypertrophy remain undetermined. Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is known to modulate the function of cardiac sarcoplasmic reticulum and play an important role in Ca(2+) cycling. We thus aimed to determine the role of CaMKII in the increased susceptibility to APD-ALT and arrhythmogenesis in the hypertrophied heart. APD was measured by high-resolution optical mapping in left ventricular (LV) anterior wall from normotensive Wistar-Kyoto (WKY; n = 10) and spontaneously hypertensive rats (SHR; n = 10) during rapid ventricular pacing. APD-ALT was evoked at significantly lower pacing rate in SHR compared with WKY (382 ± 43 vs. 465 ± 45 beats/min, P < 0.01). These changes in APD-ALT in SHR were completely reversed by KN-93 (1 μmol/l; n = 5), an inhibitor of CaMKII, but not its inactive analog, KN-92 (1 μmol/l; n = 5). The magnitude of APD-ALT was also significantly greater in SHR than WKY and was completely normalized by KN-93. Ventricular fibrillation (VF) was induced by rapid pacing more frequently in SHR than in WKY (60 vs. 10%; P < 0.05), which was also abolished by KN-93 (0%, P < 0.05). Western blot analyses indicated that the CaMKII autophosphorylation at Thr287 was significantly increased in SHR compared with WKY. The increased susceptibility to APD-ALT and VF during rapid pacing in hypertrophied heart was prevented by KN-93. CaMKII could be an important mechanism of arrhythmogenesis in cardiac hypertrophy.

Topics: Action Potentials; Animals; Anti-Arrhythmia Agents; Benzylamines; Calcium-Calmodulin-Dependent Protein Kinase Type 2; Cardiac Pacing, Artificial; Cardiomegaly; Disease Models, Animal; Heart Ventricles; Hypertension; Male; Phosphorylation; Protein Kinase Inhibitors; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Sulfonamides; Threonine; Time Factors; Ventricular Fibrillation

We studied the early pathophysiological response of lenticulostriate arterioles in rats in three models of human conditions associated with stroke: (a) chronic angiotensin II-hypertension; (b) chronic nicotine administration; (c) oxidative endothelial injury. In all three models, quantitative patch clamp analysis of freshly isolated vascular smooth muscle cells from lenticulostriate arterioles and posterior cerebral arteries showed significant increases in activity of functional L-type calcium channels that were due to an increase in open channel probability, with no change in other biophysical properties or in channel expression. In addition, all three models showed evidence of endothelial dysfunction, but of a different nature in the three. With chronic angiotensin II-hypertension, but not in the other two models, endothelial nitric oxide synthase (eNOS) was dysfunctional, was mislocalized away from its normal abluminal location, and was accumulated in peri-nuclear Golgi. By contrast, the other two models showed no mislocalization of eNOS, but instead showed evidence of oxidative stress in endothelium, with up-regulation of superoxide dismutase and hexose kinase. All three models showed significant up-regulation of expression of proliferative cell nuclear antigen (PCNA) (PCNA index, 70-80%) in arterioles in situ, which is associated with increased activation of the nuclear transcription factor, phospho-cAMP response element binding protein (phospho-CREB). In addition, calmodulin-dependent protein (CaM) kinase II was activated, in concert with the activation of L-type calcium channels. Furthermore, blockers of either L-type calcium channels (amlodipine) or of CaM kinase II (KN-93) completely prevented the activation of CREB and the up-regulation of PCNA in arterioles. Our findings demonstrate that abnormal regulation of L-type calcium channels is directly responsible for abnormal proliferative responses in vascular smooth muscle in various forms of cerebral arteriolar injury associated with endothelial dysfunction.

Topics: Amlodipine; Angiotensin II; Animals; Arterioles; Benzylamines; Brain; Calcium Channel Blockers; Calcium Channels, L-Type; Calcium-Calmodulin-Dependent Protein Kinase Type 2; Calcium-Calmodulin-Dependent Protein Kinases; Cell Division; CREB-Binding Protein; Disease Susceptibility; Endothelium, Vascular; Enzyme Inhibitors; Gene Expression Regulation; Hyperplasia; Hypertension; Models, Animal; Muscle, Smooth, Vascular; Nicotine; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nuclear Proteins; Oxidative Stress; Proliferating Cell Nuclear Antigen; Rats; Stroke; Sulfonamides; Trans-Activators