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Kenneth Richardson


Mentor: Joseph Hill, M.D./Ph.D.
Dissecting a Signaling Pathway in Cardiac Hypertrophy.

Background: Action potential prolongation underlies the heightened risk of arrhythmia in cardiac hypertrophy. The molecular basis of this action potential prolongation is poorly characterized, but prior work has implicated increased inward Ca2+ current (ICa,L). Methods and Results: To elucidate underlying molecular mechanisms, we exposed cultured cardiomyocytes to 100nM angiotensin II (Ang II). Ang II treatment (48h) induced a 71% increase in cell surface area (12,500±200 mm2 vs 7,300±500, p<0.01, mean±SEM). Voltage-clamp recordings of ICa,L in hypertrophied cells revealed a 66% increase in ICa,L density (11.1±1.5 pA/pF at +10 mV, n=11) which was increased (p<0.05) compared with control (6.7±1.6, n=12). Steady-state activation and inactivation were unchanged, and recovery from inactivation was similar. AngII-mediated increases in cell size and ICa,L were abolished by cyclosporin A, a specific inhibitor of calcineurin. Alpha1c subunit transcript and protein levels were increased in hypertrophied cells. To elucidate the role of calcineurin in hypertrophy-associated ICa,L up-regulation, we exposed cultured cardiomyocytes to adenovirus encoding constitutively active calcineurin (AdCnA, MOI 100, 48h). AdCnA induced significant (p<0.05) increases in cardiomyocyte surface area (84%) and ICa,L density (27%, 12.7±1.7 pA/pF, n=15 vs 10.0±2.1, n=10, +10mV). As protein phosphorylation is a major mechanism of hypertrophic signaling, we tested the hypothesis that Ca2+ channel phosphorylation underlies the increase in ICa,L density. Radioactive phosphate incorporation was measured in forward labeling experiments. A distinct band at 240kD, consistent with alpha1c, was detected by autoradiography in both control and AngII-treated myocytes. Cells hypertrophied by AngII demonstrated significantly decreased incorporation of 32PO4 compared with control cells (p<0.05). Discrete bands in the region of beta2 or alpha2-delta were not detected. Conclusion: Action potential prolongation in AngII-induced hypertrophy stems, at least in part, from calcineurin-mediated increases in L-type Ca2+ channel expression. Channel dephosphorylation in hypertrophy is suggested.

Abstract: "Calcineurin Signaling Modulates L-type Calcium Current in Heart: A Role in the Electrical Remodeling of Pressure-Overload Hypertrophy", J Mol Cell Cardiol May 2000 and presented at the June 2000 meeting of the International Society for Heart Research: American Section.

Publication:

Richardson KE, Tannous P, Berenji K, Nolan B, Bayless KJ, Davis GE, Rothermel BA, Hill JA. Guanosine triphosphatase activation occurs downstream of calcineurin in cardiac hypertrophy*. J Investig Med. 2005 Dec;53(8):414-24. PubMed PMID:16354580.

Wang Z, Kutschke W, Richardson KE, Karimi M, Hill JA. Electrical remodeling in pressure-overload cardiac hypertrophy: role of calcineurin. Circulation. 2001 Oct 2;104(14):1657-63. PubMed PMID: 11581145.



Honors and Awards

  • University of Iowa Pharmacology training grant 1/99 - 7/00. Predoctoral Fellowship, UI Center on Ag