Diabetes-induced activation of protein kinase C inhibits store-operated Ca 2+ uptake in rat retinal microvascular smooth muscle

Abstract

Aims/Hypothesis. To assess the effects of diabetes-induced activation of protein kinase C (PKC) on voltage-dependent and voltage-independent Ca 2+ influx pathways in retinal microvascular smooth muscle cells. Methods. Cytosolic Ca 2+ was estimated in freshly isolated rat retinal arterioles from streptozotocin-induced diabetic and non-diabetic rats using fura-2 microfluorimetry. Voltage-dependent Ca 2+ influx was tested by measuring rises in [Ca 2+ ] i with KCl (100 mmol/l) and store-operated Ca 2+ influx was assessed by depleting [Ca 2+ ] i stores with Ca 2+ free medium containing 5 µmol/l cyclopiazonic acid over 10 min and subsequently measuring the rate of rise in Ca 2+ on adding 2 mmol/l or 10 mmol/l Ca 2+ solution. Results. Ca 2+ entry through voltage-dependent L-type Ca 2+ channels was unaffected by diabetes. In contrast, store-operated Ca 2+ influx was attenuated. In microvessels from non-diabetic rats 20 mmol/l D-mannitol had no effect on store-operated Ca 2+ influx. Diabetic rats injected daily with insulin had store-operated Ca 2+ influx rates similar to non-diabetic control rats. The reduced Ca 2+ entry in diabetic microvessels was reversed by 2-h exposure to 100 nmol/l staurosporine, a non-specific PKC antagonist and was mimicked in microvessels from non-diabetic rats by 10-min exposure to the PKC activator phorbol myristate acetate (100 nmol/l). The specific PKCβ antagonist LY379196 (100 nmol/l) also reversed the poor Ca 2+ influx although its action was less efficacious than staurosporine. Conclusion/interpretation. These results show that store-operated Ca 2+ influx is inhibited in retinal arterioles from rats having sustained increased blood glucose and that PKCβ seems to play a role in mediating this effect. [Diabetologia (2003) Diabetic retinopathy is the most widespread complication of diabetes mellitus and is a major cause of blindness in the working population of developed countries. While the exact pathogenic basis of this condition remains ill-defined, it is clear that hyperglycaemia is a critical factor in its aetiology [1,2]. An early effect of hyperglycaemia is a persistent dilatation of the retinal arterioles which increases ocular blood flow and leads to downstream capillary hypertension. This is thought to contribute directly to the development and progression of the disease [3,4,5]. The angiopathy which then develops is characterised by structural changes such as pericyte [6] and arteriolar

Impairment of hepatic nuclear factor-4α binding to theStim1promoter contributes to high glucose-induced upregulation of STIM1 expression in glomerular mesangial cells

“…Diabetes/HG effects on STIM1 expression/SOC function are cell context dependent (1,3,4,30,34,58). Like in platelets and vascular endothelial cells (4,58), prolonged HG treatment in MCs increased STIM1/Orai1 protein expression levels and augmented SOCE.…”

Rho kinase and protein kinase C involvement in vascular smooth muscle myofilament calcium sensitization in arteries from diabetic rats

“…An increase in ROCK activity, enhanced production of diacylglycerols (DAG) and activation of PKC have all been shown to be associated with various vascular abnormalities, including arterial hypertension in DM (Inoguchi et al, 1992;Soloviev and Bershtein, 1992;Soloviev et al, 1998;Koya and King, 1998;Meier and King, 2000;Idris et al, 2001;Wettschureck and Offermanns, 2002;Curtis et al, 2003;Guo et al, 2003;Seko et al, 2003;Curtis and Scholfield, 2004;Ward et al, 2004;Salamanca and Khalil, 2005;Loirand et al, 2006;Das Evcimen and King, 2007). Taken together, these data suggest that the activation of ROCK and/or PKC may be causally linked to myofilaments Ca 2+ sensitization in the DM-associated hypertensive state.…”

“…Thus, both increased Ca 2+ influx and Ca 2+ release have been proposed to develop in DM and to account for the enhanced vascular reactivity. However, one controversy here is that voltage-and store-operated Ca 2+ entry channels can be, in fact, even inhibited in DM (Wang et al, 2000;Curtis et al, 2003). Alternatively, the Ca 2+ -sensitization of the contractile proteins has been proposed as a more general mechanism of elevated DM-associated vascular contractility.…”

Store-operated calcium entry and diabetic complications

“…[153][154][155][156] Curtis et al also proposed a PKCmediated pathway for the reduction of SOCE in the smooth muscle cells of retinal microvessels from STZ diabetic rats. 118 In their study, the PKC antagonist staurosporine completely restored the reduced SOCE in the diabetic vascular myocytes. 118 Further study suggested that the b isoform of PKC was responsible for the inhibition because PKCbII was specifically upregulated in diabetic retina, and an inhibitor of PKCb partially reversed the attenuated SOCE in the vascular smooth muscle cells from these diabetic rats.…”

“…The attenuated SOCE was reversed by insulin treatment (to normalize blood glucose level). 118 Using the same diabetic model, Ma et al also found an attenuated SOCE in aortic smooth muscle cells of STZ rats. 119 Importantly, the contractile response of the vessel was significantly reduced in the diabetic rats compared to that in control rats.…”