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Menopause. 2013 Oct 7. [Epub ahead of print]

Ovariectomy increases L-type calcium channel activity in porcine coronary smooth muscle.

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1
From the 1Department of Biomedical Sciences, 2Dalton Cardiovascular Research Center, and 3Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO.

Abstract

OBJECTIVE:

Sex hormone status has been demonstrated to play a role in the regulation of ion channel activity. We previously demonstrated increased L-type Ca channel current (ICa) in coronary smooth muscle cells (SMCs) of male swine compared with female swine. In male swine, endogenous testosterone increases ICa in SMCs through enhanced expression of the pore-forming α1 subunit Cav1.2. Conversely, the role of sex hormones in female swine has not been previously investigated. Therefore, the purpose of the current study was to determine the effect of ovariectomy on L-type Ca channel activity and expression in female Yucatan miniature swine.

METHODS:

Sexually mature female swine were obtained from a breeder and randomly assigned to intact female (IF; n = 5) and ovariectomized (OVX; n = 6) groups.

RESULTS:

Sensitivity to depolarization-induced contractions was increased by ovariectomy. Accordingly, L-type ICa was enhanced in OVX (-9.5 [0.6] pA/pF) versus IF (-4.5 [0.3] pA/pF) swine, although L-type Ca channel α1 subunit (Cav1.2; α1c) messenger RNA (mRNA) and protein expressions were unchanged. Of the L-type Ca channel β subunits, β1 (188 [31]) and β2a (561 [79]) had higher mRNA expression levels (target/18S) than β3 (9 [1]) and β4 (2 [0.1]). Although β2a, β3, and β4 mRNA and protein expressions were not different between groups, protein expression of the β1 subunit (Cavβ1) was decreased in OVX swine compared with IF swine.

CONCLUSIONS:

Endogenous female hormones inhibit L-type Ca channel activity in coronary SMCs potentially via the up-regulation of Cavβ1 subunit expression.

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