2. Academic Validation
  3. Chrysosplenol-C Increases Contraction by Augmentation of Sarcoplasmic Reticulum Ca2+ Loading and Release via Protein Kinase C in Rat Ventricular Myocytes

Chrysosplenol-C Increases Contraction by Augmentation of Sarcoplasmic Reticulum Ca2+ Loading and Release via Protein Kinase C in Rat Ventricular Myocytes

  • Mol Pharmacol. 2022 Jan;101(1):13-23. doi: 10.1124/molpharm.121.000365.
J Wang 1,  T N Trinh 1,  A T V Vu 1,  J C Kim 1,  A T N Hoang 1,  C J Ohk 1,  Y H Zhang 1,  C M Nguyen 1,  S H Woo 2
Affiliations

Affiliations

  • 1 Pathophysiology Laboratory, College of Pharmacy, Chungnam National University, Yuseong-gu, Daejeon, South Korea (J.W., T.N.T., A.T.V.V., S.H.W.); NEXEL Co., Ltd. 8F, 55 Magokdong-ro, Gangseo-gu, Seoul, South Korea (J.C.K.); Institute of Natural Products Chemistry, VAST, Hanoi, Vietnam (A.T.N.H., C.M.N.); and Department of Physiology and Biomedical Sciences, College of Medicine, Seoul National University, Jongro-gu, Seoul, South Korea (C.J.O., Y.H.Z.).
  • 2 Pathophysiology Laboratory, College of Pharmacy, Chungnam National University, Yuseong-gu, Daejeon, South Korea (J.W., T.N.T., A.T.V.V., S.H.W.); NEXEL Co., Ltd. 8F, 55 Magokdong-ro, Gangseo-gu, Seoul, South Korea (J.C.K.); Institute of Natural Products Chemistry, VAST, Hanoi, Vietnam (A.T.N.H., C.M.N.); and Department of Physiology and Biomedical Sciences, College of Medicine, Seoul National University, Jongro-gu, Seoul, South Korea (C.J.O., Y.H.Z.) [email protected].
PMID: 34764211 DOI: 10.1124/molpharm.121.000365
Abstract

Naturally found chrysosplenol-C (4',5,6-trihydroxy-3,3',7-trimethoxyflavone) increases the contractility of cardiac myocytes independent of β-adrenergic signaling. We investigated the cellular mechanism for chrysosplenol-C-induced positive inotropy. Global and local CA2+ signals, L-type CA2+ current (ICA), and contraction were measured from adult rat ventricular myocytes using two-dimensional confocal CA2+ imaging, the whole-cell patch-clamp technique, and video-edge detection, respectively. Application of chrysosplenol-C reversibly increased CA2+ transient magnitude with a maximal increase of ∼55% within 2- to 3-minute exposures (EC50 ≅ 21 μM). This chemical did not alter ICA and slightly increased diastolic CA2+ level. The frequency and size of resting CA2+ sparks were increased by chrysosplenol-C. Chrysosplenol-C significantly increased sarcoplasmic reticulum (SR) CA2+ content but not fractional release. Pretreatment of protein kinase C (PKC) inhibitor but not CA2+/calmodulin-dependent protein kinase II (CaMKII) inhibitor abolished the stimulatory effects of chrysosplenol-C on CA2+ transients and CA2+ sparks. Chrysosplenol-C-induced positive inotropy was removed by the inhibition of PKC but not CaMKII or Phospholipase C. Western blotting assessment revealed that PKC-δ protein level in the membrane fractions significantly increase within 2 minutes after chrysosplenol-C exposure with a delayed (5-minute) increase in PKC-α levels in insoluble membrane. These results suggest that chrysosplenol-C enhances contractility via PKC (most likely PKC-δ)-dependent enhancement of SR CA2+ releases in ventricular myocytes. SIGNIFICANCE STATEMENT: Study shows that chrysosplenol-C, a natural flavone showing a positive inotropic effect, increases SR CA2+ releases on depolarizations and CA2+ sparks with an increase of SR CA2+ loading but not L-type CA2+ current in ventricular myocytes. Chrysosplenol-C-induced enhancement in contraction is eliminated by PKC inhibition, and it is associated with redistributions of PKC to the membrane. These indicate that chrysosplenol-C enhances contraction via PKC-dependent augmentations of SR CA2+ release and CA2+ loading during action potentials.

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