Insulin treatment enhances AT₁receptor function in OK cells

Abstract

Increased renal sodium retention is considered a major risk factor contributing to hypertension associated with chronic hyperinsulinemia and obesity. However, the molecular mechanism involved is not understood. The present study investigates the effect of insulin treatment on AT1 receptor expression and ANG II-induced stimulation of Na/H exchanger (NHE) and Na-K-ATPase (NKA) in opossum kidney (OK) cells, a proximal tubule cell line. The presence of the AT1 receptors in OK cells was confirmed by the specific binding of 125I-sar-ANG II and by detecting approximately 43-kDa protein on Western blot analysis with AT1 receptor antibody and blocking peptide as well as by expression of AT1 receptor mRNA as determined by RT-PCR. Insulin treatment (100 nM for 24 h) caused an increase in 125I-sar-ANG II binding, AT1 receptor protein content, and mRNA levels. The whole cell lysate and membrane showed similar insulin-induced increase in the AT1 receptor protein expression, which was blocked by genistein (100 nM), a tyrosine kinase inhibitor, and cycloheximide (1.5 microg/ml), a protein synthesis inhibitor. Determination of ethyl isopropyl amiloride-sensitive 22Na+ uptake, a measure of the NHE activity, revealed that ANG II (1-100 pM)-induced stimulation of NHE in insulin-treated cells was significantly greater than in the control cells. Similarly, ANG II (1-100 pM)-induced stimulation of ouabain-sensitive 86Rb+ uptake, a measure of NKA activity in insulin-treated cells, was significantly greater than in the control cells. ANG II stimulation of both the transporters was blocked by AT1 receptor antagonist losartan, suggesting the involvement of AT1 receptors. Thus chronic insulin treatment causes upregulation of AT1 receptors, which evoked ANG II-induced stimulation of NHE and NKA. We propose that insulin-induced increase in the renal AT1 receptor function serves as a mechanism responsible for the increased renal sodium reabsorption and thus may contribute to development of hypertension in conditions associated with hyperinsulinemia.

The multi‐faceted cross‐talk between the insulin and angiotensin II signaling systems

“…Thus, Nickenig and colleagues [86] observed that an acute treatment with insulin promotes a significant increase of AT 1 protein expression in vascular smooth muscle cells. Similarly, Banday and coworkers [87] observed an increase of AT 1 expression and Ang II action upon Na-K-ATPase and Na/H exchanger proteins in renal cells. Finally, Golovchanko and colleagues [88] have shown that hyperinsulinemia enhances Ang II-induced NF-kappaB transcriptional activity in vascular smooth muscle cells.…”

Enhanced AT1receptor-mediated vasocontractile response to ANG II in endothelium-denuded aorta of obese Zucker rats

“…The antibody used for AT 1 receptors recognized a single band of ϳ45 kDa (Fig. 5A), which has earlier been characterized for its specificity (3). Similarly, the antibody used for eNOS detected a single band of ϳ133 kDa (Fig.…”

Insulin improves cardiomyocyte contractile function through enhancement of SERCA2a activity in simulated ischemia/reperfusion1

“…Insulin (10 -7 mol/L, the concentration used in most in vitro studies) [20,21] exerted significant inotropic action in normal myocytes (21.8%±0.5% of Con+Ins group vs 17.9%± 0.8% of Con group; P<0.05, n=20 myocytes from 8 hearts) ( Table 1). Although the contractile function of simulated I/R myocytes (underdoing ischemia for 15 min and reperfusion with Tyrode's solution for 30 min) could not completely recover to the level of the control group, in which the cells were perfused with Tyrode's solution for 45 min, there was no significant difference in contraction of the cells in the two groups (17.9%±0.8% of Con group vs 14.5%±0.7% of I/R group; P>0.05, n=20 myocytes from 8 hearts).…”