title: Sex differences in SR Ca(2+) release in murine ventricular myocytes are regulated by the cAMP/PKA pathway.
abstract: Previous studies have shown that ventricular myocytes from female rats have smaller contractions and Ca(2+) transients than males. As cardiac contraction is regulated by the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) pathway, we hypothesized that sex differences in cAMP contribute to differences in Ca(2+) handling. Ca(2+) transients (fura-2) and ionic currents were measured simultaneously (37°C, 2Hz) in ventricular myocytes from adult male and female C57BL/6 mice. Under basal conditions, diastolic Ca(2+), sarcoplasmic reticulum (SR) Ca(2+) stores, and L-type Ca(2+) current did not differ between the sexes. However, female myocytes had smaller Ca(2+) transients (26% smaller), Ca(2+) sparks (6% smaller), and excitation-contraction coupling gain in comparison to males (23% smaller). Interestingly, basal levels of intracellular cAMP were lower in female myocytes (0.7±0.1 vs. 1.7±0.2fmol/μg protein; p<0.001). Importantly, PKA inhibition (2μM H-89) eliminated male-female differences in Ca(2+) transients and gain, as well as Ca(2+) spark amplitude. Western blots showed that PKA inhibition also reduced the ratio of phospho:total RyR2 in male hearts, but not in female hearts. Stimulation of cAMP production with 10μM forskolin abolished sex differences in cAMP levels, as well as differences in Ca(2+) transients, sparks, and gain. To determine if the breakdown of cAMP differed between the sexes, phosphodiesterase (PDE) mRNA levels were measured. PDE3 expression was similar in males and females, but PDE4B expression was higher in female ventricles. The inhibition of cAMP breakdown by PDE4 (10μM rolipram) abolished differences in Ca(2+) transients and gain. These findings suggest that female myocytes have lower levels of basal cAMP due, in part, to higher expression of PDE4B. Lower cAMP levels in females may attenuate PKA phosphorylation of Ca(2+) handling proteins in females, and may limit positive inotropic responses to stimulation of the cAMP/PKA pathway in female hearts.
authors: Department of Pharmacology, Faculty of Medicine, Dalhousie University, 5850 College Street, P.O. Box 15000, Halifax B3H 4R2, Nova Scotia, Canada. Electronic address: Randi.Parks@dal.ca.
authors: Randi J
authors: RJ
authors: Parks
authors: Physiology and Biophysics, Faculty of Medicine, Dalhousie University, 5850 College Street, P.O. Box 15000, Halifax B3H 4R2, Nova Scotia, Canada. Electronic address: Giban.Ray@dal.Ca.
authors: Gibanananda
authors: G
authors: Ray
authors: Department of Physiology, University of Melbourne, Parkville VIC 3010, Australia. Electronic address: L.Bienvenu@student.unimelb.edu.au.
authors: Laura A
authors: LA
authors: Bienvenu
authors: Physiology and Biophysics, Faculty of Medicine, Dalhousie University, 5850 College Street, P.O. Box 15000, Halifax B3H 4R2, Nova Scotia, Canada. Electronic address: Robert.Rose@dal.ca.
authors: Robert A
authors: RA
authors: Rose
authors: Department of Pharmacology, Faculty of Medicine, Dalhousie University, 5850 College Street, P.O. Box 15000, Halifax B3H 4R2, Nova Scotia, Canada; Medicine (Geriatric Medicine), Faculty of Medicine, Dalhousie University, 5850 College Street, P.O. Box 15000, Halifax B3H 4R2, Nova Scotia, Canada. Electronic address: Susan.Howlett@dal.ca.
authors: Susan E
authors: SE
authors: Howlett
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4 / Q000235:genetics / Q000378:metabolism; D003971:Diastole; D004789:Enzyme Activation; D056966:Excitation Contraction Coupling; D005260:Female; D006352:Heart Ventricles / Q000166:cytology*; D042541:Intracellular Space / Q000378:metabolism; D015640:Ion Channel Gating; D008297:Male; D008810:Mice, Inbred C57BL; D032383:Myocytes, Cardiac / Q000378:metabolism*; D010766:Phosphorylation; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D012727:Sex Characteristics; D015398:Signal Transduction
chemical_list: D012333:RNA, Messenger; D019837:Ryanodine Receptor Calcium Release Channel; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; C543000:PDE4B protein, mouse; D000262:Adenylyl Cyclases; D002118:Calcium
keywords: Calcium spark; Calcium transient; Excitation–contraction coupling; Gain; Gender; Phosphodiesterase