Gender differences in the regulation of renal arteries from normotensive and hypertensive rats

H. Figueiredo Galvao, I. A. Greenwood. Vascular Biology Research Centre, St. George's, University of London, London, United Kingdom.

Introduction: Hypertension is a major risk factor for a number of cardiovascular diseases (1). Kv7 channels contribute to resting membrane potential in vascular smooth muscle cells and their role in vascular tone has been identified (2). However, their role in the female vasculature has not been investigated. This study aims to compare the expression and function of Kv7 channels in the renal artery vasculature of female Wistar rats (WT) and SHRs against that of males.

Methods: qRT-PCR was used to determine the mRNA expression of KCNQ1, KCNQ4 and KCNE4, as well as miRNA 153. Relative protein expression of Kv7.1, Kv7.4 and KCNE4 were determined using Western Blots normalised to β-actin. Dose-response curves using Methoxamine (10nM-30μM), ML213 (100nM-10μM), ML277 (10nM-10μM), ANP (10pM-30nM) and Isoprenaline (1nM-3μM) were performed using small vessel myography.

Results: Kv7.1 protein expression decreased in the hypertensive models with no sex-dependent differences. No significant Kv7.4 protein expressions were observed between male and female WTs, however, female SHRs expressed 3-fold higher Kv7.4 protein levels than male SHRs (p<0.05; n=5). Female SHRs expressed 3-fold higher KCNE4 protein levels than male SHRs (p<0.05; n≥4). No significant differences were observed in the renal artery response of male and female WTs to Methoxamine, however, female SHRs displayed a 2-fold decreased sensitivity to Methoxamine (p<0.0001; n≥5) than male SHRs. Female WTs were 2-fold more sensitive to ANP (p<0.006; n≥5) than male WTs, while female SHRs were 3-fold more sensitive than male SHRs to ANP (p<0.0032; n≥5). Female WTs and female SHRs were both 2-fold more sensitive to the Kv7.1 activator ML277 than their respective male counterparts (p<0.0002 and p<0.001, respectively; n≥4). Male WTs were 10-times more sensitive to Isoprenaline than female WTs (p<0.0001; n=5), despite female WTs being 2-fold more sensitive to the Kv7.2-7.5 activator ML213 (p<0.0001; n≥5) than male WTs. The male SHR response to Isoprenaline was abrogated, a result in-line with its abrogated ML213 response. The abrogated female SHR response to Isoprenaline is discordant with its response to ML213, achieving an EC₅₀(3.05μM) parallel to that of a WT male (2.98μM).

Conclusions: This study provides evidence for a differential expression and function of Kv7 channels in the female vasculature. The Isoprenaline-mediated vasorelaxations in the female renal artery suggest the involvement of additional Kv7 channels in β-adrenoceptor mediated vasorelaxations.

References:

1) Gudmundsdottir et al. (2012). Therapeutic Advances in Chronic Diseases. 3(3):137-46.

2) Sobey (2001). Arteriosclerosis, Thrombosis and Vascular Biology. 21:28-38.