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CARDIOVASCULAR

Effects of Phytoestrogens on Sarcoplasmic/Endoplasmic Reticulum Calcium ATPase 2a and Ca²⁺ Uptake into Cardiac Sarcoplasmic Reticulum

Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada (M.L.O., M.E.K., G.J.K.); Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts (T.W.H.); and Department of Physiology, Queens University, Kingston, Ontario, Canada (C.A.W.)

Phytoestrogens are naturally occurring estrogenic compounds found in plants and plant products. These compounds are also known to exert cellular effects independent of their interactions with estrogen receptors. We studied the effects of the phytoestrogens phloretin, phloridzin, genistein, and biochanin A on Ca²⁺ uptake into the cardiac muscle sarcoplasmic reticulum (SR). Genistein and biochanin A did not affect SR Ca²⁺ uptake. On the other hand, phloretin and phloridzin decreased the maximum velocity of SR Ca²⁺ uptake but did not affect the Hill coefficient or the Ca²⁺ sensitivity of uptake. Measurements of the ATPase activity of the cardiac SR Ca²⁺ pump (SERCA2a) revealed direct inhibitory effects of phloretin and phloridzin on SERCA2a. Neither compound induced a detectable change in the permeability of the SR membrane to Ca²⁺. These results indicate that phloretin and phloridzin inhibit cardiac SR Ca²⁺ uptake by directly inhibiting SERCA2a.

Address correspondence to: Dr. Gary Kargacin, Department of Physiology and Biophysics, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N 4N1, Canada. E-mail: kargacin{at}ucalgary.ca

This article has been cited by other articles:

				M. L. Olson, M. E. Kargacin, C. A. Ward, and G. J. Kargacin Effects of Phloretin and Phloridzin on Ca2+ Handling, the Action Potential, and Ion Currents in Rat Ventricular Myocytes J. Pharmacol. Exp. Ther., June 1, 2007; 321(3): 921 - 929. [Abstract] [Full Text] [PDF]