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Sex difference in cardiomyocyte function in normal and metallothionein transgenic mice: the effect of diabetes mellitus

Division of Pharmaceutical Sciences and Center for Cardiovascular Research and Alternative Medicine, University of Wyoming, Laramie, Wyoming

Submitted 4 October 2005 ; accepted in final form 4 January 2006

Evidence suggests a sex difference in intrinsic physiological and diabetic myocardial contractile function related to antioxidant properties of female ovarian hormones. This study was designed to examine the effect of cardiac overexpression of antioxidant metallothionein on intrinsic and diabetic cardiomyocyte function. Weight-matched wild-type (FVB) and metallothionein transgenic mice of both sexes were made diabetic with streptozotocin (220 mg/kg). Contractile and intracellular Ca²⁺ properties were evaluated including peak shortening (PS), time to PS, time to 90% relengthening (TR₉₀), maximal velocity of shortening or relengthening (±dL/dt), fura-2 fluorescence intensity change, and Ca²⁺ decay rate. Akt and transcription factor c-Jun levels were evaluated by Western blot. Myocytes from female FVB mice exhibited lower PS, ±dL/dt, and fura-2 fluorescence intensity change, prolonged time to PS, TR₉₀, and Ca²⁺ decay compared with male FVB mice. Interestingly, this sex difference was not present in metallothionein mice. Diabetes depressed PS, ±dL/dt and caffeine-induced Ca²⁺ release, as well as prolonged TR₉₀ and Ca²⁺ decay in male FVB mice, whereas it only reduced PS in female FVB mice. These diabetic dysfunctions were nullified by metallothionein in both sexes. Females displayed elevated Akt phosphorylation and reduced c-Jun phosphorylation. Diabetes dampened Akt phosphorylation in male FVB mice and enhanced c-Jun in both sexes. Diabetes-induced alterations in Akt phosphorylation and c-Jun were abolished by metallothionein. The sex difference in Akt phosphorylation but not c-Jun levels was reversed by metallothionein. These data indicate that antioxidant capacity plays an important role in sex differences in both intrinsic and diabetic cardiomyocyte contractile properties possibly related to phosphorylation of Akt and c-Jun.

myocyte shortening; Akt; c-Jun

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