Alteration of cytosolic calcium induced by angiotensin II and norepinephrine in mesangial cells from diabetic rats

Abstract

To evaluate functional alterations of mesangial cells induced by diabetes (DMC), we observed the changes of cytosolic calcium ([Ca]i) in response to the vasoconstrictor agonists angiotensin II (Ang II) and norepinephrine (NOR). DMC were obtained from rats with streptozotocin-induced diabetes, cultured in normal medium and identified as mesangial cells (MC) in the third subculture. [Ca]i was measured using fura-2 as a fluorophore. Basal calcium levels (60 to 80 nM) in DMC were not different from control mesangial cells (CMC). The high glucose (30 mM) medium concentration reduced the response of CMC and DMC to Ang II and NOR. This was not an osmotic effect since mannitol did not alter these responses. When DMC were stimulated with Ang II, a desensitized response was always observed, with a transient variation of [Ca]i (N = 6, P < 0.05). In contrast, a non-desensitized response with a sustained pattern of [Ca]i increases was obtained in NOR-stimulated DMC. Therefore, the present results suggest that DMC show a modified response to stimulation of the Ang II receptor, which is expressed phenotypically in culture by desensitization. Furthermore, these alterations induced by diabetes environment in MC in vivo were maintained in vitro despite a long period (approximately 5 months) in which the cells were grown in normal culture medium.

High Glucose Levels Alter Angiotensin II-Induced Ca²⁺ Uptake via PKC and cAMP Pathways in Renal Proximal Tubular Cells

“…At high glucose concentrations, Cl -and nonselective cation channel stimulation by ANG II was attenuated (!7-fold) [34]. Hadad et al [16] The present study demonstrated that PKC and cAMP signal pathways are involved in the alterations of Ca 2+ uptake by ANG II in PTCs grown under high-glucose conditions. PKC activation may be due to an increase of sn-1,2-diacylglycerol formation from glucose metabolism, since sn-1,2-diacylglyerol or 1-oleoyl-2-acetyl-sn-glycerol, PKC activators, also induced stimulation of Ca 2+ uptake [25].…”

“…In mesangial cells, high glucose concentrations increased intracellular cAMP levels, and cAMP analogs mimicked high-glucose action on mitogen-activated protein kinase activation or collagen synthesis [14,15]. These recent investigations lend further support to the notion that changes of [Ca 2+ ] i due to high glucose or ANG II via PKC or cAMP play an important role in diabetic nephropathy [16][17][18]. However, the alterations of the Ca 2+ uptake induced by ANG II in the renal PTCs under diabetic conditions are not fully elucidated.…”

Tubular and Interstitial Cell Apoptosis in the Streptozotocin-Diabetic Rat Kidney

“…Although the effects of these peptides on cell growth are unclear, it is of interest that Ang IV has been shown to inhibit apoptosis in neuronal cells [50]. In addition to these pathways, hyperglycemia has been reported to either augment [51]or attenuate [52]Ang-II-mediated cell signaling pathways, suggesting the possibility that altered AT 1 or AT 2 receptor signaling could contribute to the stimulation of apoptosis in the diabetic kidney.…”

Canonical transient receptor potential channels in diabetes

“…20, 22 In diabetes, mesangial contractile function is impaired, and reduced Ca 2+ influx is believed to be a major contributing factor to the hypocontractility. 24–26 Our functional studies in cultured mesangial cells have demonstrated that both TRPC1 and TRPC6 participate in agonist-stimulated Ca 2+ entry through store-operated and/or receptor-operated mechanisms. 20, 22 It is known that different TRPC isoforms can interact with each other to form heteromeric channels, 27, 28 We have previously shown that TRPC1 and TRPC6 were colocalized and physically interacted with each other in mesangial cells.…”