title: Myofilament response to Ca2+ and Na+/H+ exchanger activity in sex hormone-related protection of cardiac myocytes from deactivation in hypercapnic acidosis.
abstract: Compared to sham-operated controls, myofilaments from hearts of ovariectomized (OVX) rats demonstrate an increase in Ca2+ sensitivity with no change in maximum tension (Wattanapermpool J and Reiser PJ. Am J Physiol 277: H467-H473, 1999). To test the significance of this modification in intact cells, we compared intracellular Ca2+ transients and shortening of ventricular myocytes isolated from sham and 10-wk OVX rats. There was a decrease in the peak Ca2+ transient with prolonged 50% decay time in OVX cardiac myocytes without changes in the resting intracellular Ca2+ concentration. Percent cell shortening was also depressed, and relaxation was prolonged in cardiac myocytes from OVX rats compared with shams. Ovariectomy induced a sensitization of the myofilaments to Ca2+. Hypercapnic acidosis suppressed the shortening of OVX myocytes to a lesser extent than that detected in shams. Moreover, a larger compensatory increase in %cell shortening was obtained in OVX myocytes during prolonged acidosis. The elevated compensation in cell shortening was related to a higher amount of increase in the amplitude of the Ca2+ transient in OVX myocytes. However, these differences in Ca2+ transients and %cell shortening were no longer evident in the presence of 1 microM cariporide, a specific inhibitor of Na+/H+ exchanger type 1 (NHE1). Our results indicate that deprivation of female sex hormones modulates the intracellular Ca2+ concentration in cardiac myocytes, possibly via an increased NHE1 activity, which may act in concert with Ca2+ hypersensitivity of myofilament activation as a determinant of sex differences in cardiac function.
authors.affiliation: Department of Physiology and Biophysics, Medicine and Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, 835 S. Wolcott Ave., Chicago, IL 60612-7342, USA.
authors.forename: Tepmanas
authors.initials: T
authors.lastname: Bupha-Intr
authors.forename: Jonggonnee
authors.initials: J
authors.lastname: Wattanapermpool
authors.forename: James R
authors.initials: JR
authors.lastname: Peña
authors.forename: Beata M
authors.initials: BM
authors.lastname: Wolska
authors.forename: R J
authors.initials: RJ
authors.lastname: Solaro
mesh_terms: D000142:Acidosis, Respiratory / Q000503:physiopathology*; D008841:Actin Cytoskeleton / Q000502:physiology*; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology; D002469:Cell Separation; D004967:Estrogens / Q000494:pharmacology; D005260:Female; D012739:Gonadal Steroid Hormones / Q000494:pharmacology*; D006146:Guanidines / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D006935:Hypercapnia / Q000503:physiopathology*; D066298:In Vitro Techniques; D007700:Kinetics; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D009200:Myocardial Contraction / Q000502:physiology; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000502:physiology*; D010052:Ovariectomy; D051381:Rats; D017207:Rats, Sprague-Dawley; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013450:Sulfones / Q000494:pharmacology
chemical_list: D000889:Anti-Arrhythmia Agents; D004967:Estrogens; D012739:Gonadal Steroid Hormones; D006146:Guanidines; D019831:Sodium-Calcium Exchanger; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; C093373:cariporide; D002118:Calcium