Abstract 14590: CaMKII Inhibition in Smooth Muscle Regulates Calcium Homeostasis and Improves Angiotensin Ii- Hypertension
Background: The multifunctional calcium/calmodulin-dependent kinase II (CaMKII) is expressed in vascular smooth muscle cells (VSMC) and activated by Angiotensin-II (Ang-II). We hypothesized that CaMKII in VSMC mediates Ang-II hypertension.
Methods: To test this hypothesis, we developed transgenic mice that express the specific CaMKII peptide inhibitor CaMKIIN selectively in VSMC (Tg SM CaMKIIN).
Results: Tg SM CaMKIIN mice have a 65% reduced CaMKII activity in arteries (p<0.01) and identical baseline blood pressure by radiotelemetry compared to littermates. Following Ang-II infusion (1.25 μ g/kg/min) for 14 days, the increase in mean pressure was significantly attenuated in Tg SM CaMKIIN mice (129±4 mmHg vs, 116±3 mmHg, p<0.05). Mesenteric arteries from transgenic mice exhibited altered vasoconstriction and decreased MLC20 phosphorylation (p<0.05). Ang-II increases Ca2+ influx through L-type Ca2+ channels (LTCC). Compared with littermates, freshly isolated mesenteric VSMC of Ang-II infused Tg SM CaMKIIN mice had significantly reduced (6.5 ± 0.3 pA/ pF vs 5.0 ± 0.3 pA/pF; p<0.05) voltage gated L-type Ca2+ current (ICa) (by whole cell patch) and ICa facilitation. Moreover, the [Ca2+]i response to Ang-II (by fura-2) was reduced by 50 % in mesenteric Tg SM CaMKIIN VSMC compared to control (28 ± 3% Vs, 14 ± 2%; p<0.05) and the total releasable SR Ca2+ by 35 % (p<0.05). Phospholamban (PLB), a specific CaMKII target, regulates SR Ca2+ ATPase (SERCA2) activity and thereby SR Ca2+ load. Immunoblots showed a significant reduction of PLB phosphorylation in mesenteric arteries of transgenic mice at baseline and after Ang-II infusion (70 % and 65% respectively, p<0.05) compared to controls. SERCA2 activity, assessed by inorganic phosphate release was reduced in transgenic mice at baseline (770±104 vs, 581±63 nmoles Pi, p<0.05) and after Ang-II infusion (1458±160 vs, 692±70, nmoles Pi, p<0.05).
Conclusion: Inhibition of CaMKII in VSMC significantly attenuates Ang-II induced hypertension through regulation of LTCC function and calcium homeostasis. CaMKII may be a novel target in treating hypertension.
- © 2012 by American Heart Association, Inc.