Reduced EDHF responses and connexin activity in mesenteric arteries from the insulin-resistant obese Zucker rat

Abstract

Aims/hypothesis The objective of this study was to examine the effect of insulin resistance on endothelium-derived hyperpolarising factor (EDHF) and small mesenteric artery endothelial function using 25-week-old insulin-resistant obese Zucker rats (OZRs) and lean littermate control rats (LZRs). The involvement of gap junctions and their connexin subunits in the EDHF relaxation response was also assessed. Methods Mesenteric arteries were evaluated using the following assays: (1) endothelial function by pressure myography, with internal diameter recorded using video microscopy; (2) connexin protein levels by western blotting; and (3) Cx mRNA expression by real-time PCR. Results Relaxations in response to acetylcholine were significantly smaller in mesenteric arteries from the OZRs than the LZRs, whereas there was no difference in relaxations in response to levcromakalim. Responses to acetylcholine were not altered by nitric oxide inhibitors, but were abolished by charybdotoxin in combination with apamin, which blocked the EDHF component of the response. 40 Gap27 significantly attenuated the response to acetylcholine in the LZRs, but had no effect in the OZRs. Connexin 40 protein and Cx40 mRNA levels in mesenteric vascular homogenates were significantly smaller in the OZRs than in the LZRs, with no difference in connexin 43 or Cx43 mRNA levels. Conclusions/interpretation These findings demonstrate that endothelial dysfunction in mesenteric arteries from the insulin-resistant OZRs can be attributed to a defect in EDHF. The results also suggest that the defective EDHF is at least partly related to an impairment of connexin 40-associated gap junctions, through a decrease in connexin 40 protein and Cx40 mRNA expression in the OZRs.

Altered gap junctional communication and renal haemodynamics in Zucker fatty rat model of type 2 diabetes

“…The present findings that Cx40 GAP27 and Cx37,43 GAP27, but not Cx43 GAP26 diminished renal autoregulation in ZL rats support the idea that gap junctions comprising Cx37 and Cx40 transduce TGFback signals. Although our immunohistochemical studies did not reveal differences in Cx40 content between ZL and ZDF rats, we did demonstrate that the density of abundance of Cx37 in renin-secreting cells was decreased in ZDF rats, at least in part accounting for abnormal renal autoregulation in these animals.…”

“…The present results raise the possibility that myogenic response is also attenuated in diabetes. In combination with reduced abundance and enhanced phosphorylation of Cxs, the finding that Cx40 GAP27 and Cx37,43 GAP27 failed to induce further changes in renal autoregulation in ZDF rats constitutes novel evidence that gap junctions composed of Cx37 and Cx40 were already malfunctioning in ZDF rats, suggesting that Cxs form a link between biochemical alterations and pathophysiological derangements in diabetic nephropathy.…”

“…Interestingly, phosphorylated Cxs are prone to be ubiquitinated to degrade [37]. Reductions of Cx40 and weakened effects of endothelium-derived hyperpolarising factor (EDHF) have been demonstrated in the mesenteric artery of Zucker obese rats [43]. Cxs play an important role in myogenic response [44], one of the mechanisms mediating renal autoregulation [45].…”

Low intrinsic exercise capacity in rats predisposes to age-dependent cardiac remodeling independent of macrovascular function

“…Although differences in NOS expression were not determined in the present study, our findings indicate that there were no phenotype differences in vascular NOS activity. Rather, these data suggest that impairment at the level of EDHF-type relaxation mediates microvascular dysfunction in LCR rats, which is in accordance with settings of type 2 diabetes, where EDHF-dependent responses are similarly impaired in resistance arteries (2,51).…”

Connexins and gap junctions in the EDHF phenomenon and conducted vasomotor responses

“…A single abnormality seems unlikely, however, because there may be increased cAMP hydrolysis by type 3 phosphodiesterase, reduced generation of cAMP secondary to impaired activity of adenylate cyclases types 5/6, and impaired PKA function, possibly resulting from altered catalytic and regulatory subunit expression [125][126][127][128]. Furthermore, abnormalities in other essential components of the EDHF pathway such as impaired SK Ca channel function and reduced Cx40 expression have also been described [20,208].…”