ATP-sensitive potassium channel (K(ATP )channel) expression in the normal canine pancreas and in canine insulinomas

BACKGROUND: Pancreatic beta cells express ATP-sensitive potassium (K(ATP)) channels that are needed for normal insulin secretion and are targets for drugs that modulate insulin secretion. The K(ATP )channel is composed of two subunits: a sulfonylurea receptor (SUR 1) and an inward rectifying potassium channel (Kir(6.2)). K(ATP )channel activity is influenced by the metabolic state of the cell and initiates the ionic events that precede insulin exocytosis. Although drugs that target the K(ATP )channel have the expected effects on insulin secretion in dogs, little is known about molecular aspects of this potassium channel. To learn more about canine beta cell K(ATP )channels, we studied K(ATP )channel expression by the normal canine pancreas and by insulin-secreting tumors of dogs. RESULTS: Pancreatic tissue from normal dogs and tumor tissue from three dogs with histologically-confirmed insulinomas was examined for expression of K(ATP )channel subunits (SUR1 and Kir(6.2)) using RT-PCR. Normal canine pancreas expressed SUR1 and Kir(6.2 )subunits of the K(ATP )channel. The partial nucleotide sequences for SUR1 and Kir(6.2 )obtained from the normal pancreas showed a high degree of homology to published sequences for other mammalian species. SUR1 and Kir(6.2 )expression was observed in each of the three canine insulinomas examined. Comparison of short sequences from insulinomas with those obtained from normal pancreas did not reveal any mutations in either SUR1 or Kir(6.2 )in any of the insulinomas. CONCLUSION: Canine pancreatic K(ATP )channels have the same subunit composition as those found in the endocrine pancreases of humans, rats, and mice, suggesting that the canine channel is regulated in a similar fashion as in other species. SUR1 and Kir(6.2 )expression was found in the three insulinomas examined indicating that unregulated insulin secretion by these tumors does not result from failure to express one or both K(ATP )channel subunits

L225P mutation of ABCC8 gene: a case of transient neonatal diabetes mellitus with thrombophilic predisposition and epilepsy

Neonatal diabetes mellitus (NDM) is defined as a rare disorder of glucose metabolism in the first six months of life, transient (TNDM) or permanent (PNDM). TNDM usually resolves by 18 months, though it might relapse later in life; PNDM requires lifelong therapy with insulin or/and sulfonylurea. Etiology of NDM is monogenic and genetically heterogeneous. TNDM is often caused by an over-expression of paternal genes on chromosome 6 or by mutation in KCNJ11. Either way the release of insulin is reduced. PNDM is mostly associated with two genes, KCNJ11and ABCC8, which encode, respectively, Kir 6.2 and SUR1, subunits of beta cells K-ATP channel. K-ATP channel is constitutively open, hyperglycemia increases the intracellular ATP levels that cause the closure of K-ATP channel and the depolarization of beta cell causing release of insulin. Inactivating mutations in Kir 6.2 or SUR1, K-ATP channel remains open leading to impaired insulin secretion and neonatal diabetes. Here, we report a case of a three months old baby with diagnosis of NDM and thrombophilic predisposition, referred to emergency pediatric department because of intercurrent ipsilateral clonus to the upper and lower right limbs from a few days, successor seizures during the recovery and incidental finding of hyperglycemia. Child was initially treated with insulin, subsequently was started therapy with glybenclamide for 13 months with progressive decal age. The child was also successfully weaned by treatment with sulfonylureas and epilepsy was well controlled with Phenobarbital

K-ATP channel gene expression is induced by urocortin and mediates its cardioprotective effect

Background-Urocortin is a novel cardioprotective agent that can protect cardiac myocytes from the damaging effects of ischemia/reperfusion both in culture and in the intact heart and is effective when given at reperfusion.Methods and Results-We have analyzed global changes in gone expression in cardiac myocytes after urocortin treatment using gene chip technology. We report that urocortin specifically induces enhanced expression of the Kir 6.1 cardiac potassium channel subunit. On the basis of this finding, we showed that the cardioprotective effect of urocortin both in isolated cardiac cells and in the intact heart is specifically blocked by both generalized and mitochondrial-specific K-ATP channel blockers, whereas the cardioprotective effect of cardiotrophin-1 is unaffected. Conversely, inhibiting the Kir 6.1 channel subunit greatly enhances cardiac cell death after ischemia.Conclusions-This is, to our knowledge, the first report of the altered expression of a K-ATP. channel subunit induced by a cardioprotective agent and demonstrates that K-ATP, channel opening is essential for the effect of this novel cardioprotective agent

Alteration of Loperamide-Induced Prostate Relaxation in High-Fat Diet-Fed Rats

Objective. To investigate the change of loperamide-induced prostate relaxation in rats fed with high-fat diet (HFD). Materials and Methods. Adult male Wistar rats were divided into 2 groups: (1) control rats fed with normal chow and (2) rats fed with HFD for 6 months. The prostate was removed for histology study. Isolated prostate strips were hung in organ bath and precontracted with 1 μmol/L phenylephrine or 50 mmol/L KCl. The relaxation responses to loperamide 0.1 to 10 μmol/L were recorded. Western blotting analyses were performed for prostate μ-opioid receptors (MOR) and ATP-sensitive potassium (KATP) channel proteins: sulfonylurea receptor (SUR) and inwardly rectifying potassium channel (Kir) 6.2 subunits. Results. Body weight, prostate weight, plasma levels of glucose, insulin, triglyceride, and cholesterol, as well as systolic blood pressure, were significantly increased in the HFD rats. Histology showed prostatic hyperplasia in the HFD rat prostate. Prostatic relaxation induced by loperamide was markedly reduced in HFD when compared to the control. Protein expressions of MOR, SUR, and Kir 6.2 were decreased in HFD-fed rats. Conclusion. Loperamide-induced prostate relaxation is decreased in HFD rats due to reduced MOR and KATP channel expressions

Prostatic Relaxation Induced by Loperamide Is Reduced in Spontaneously Hypertensive Rats

This paper shows a new finding about the decrease of relaxative response to loperamide in prostate of spontaneously hypertensive rats (SHR) as compare to normal rats (WKY). Authors demonstrated the reduction of ATP-sensitive potassium channels is resposible for this change using immunoblotting analysis and the decrease of action induced by diazoxide. This view is not mentioned before and is the first one reporting this result

Inward rectifier potassium current in dopaminergic periglomerular cells of mouse olfactory bulb.

openInward rectifier potassium (Kir) channels are important for neuronal signalling and membrane excitability. In this work, patch-clamp techniques were used to characterize Kir channels in mouse dopaminergic (DA) periglomerular (PG) cells. These interneurons are critically placed at the entry of the bulbar circuitry, in contact with terminals of olfactory sensory neurons and with dendrites of projection neurons. Perforated-patch configuration was adopted to record Kir current in DA-PG cells in thin slice. IKir could be distinguished from the hyperpolarization-activated current by showing full activation in < 10 ms, no inactivation, suppression by Ba2+ in a typical voltage-dependent manner and reversal potential nearly coincident with EK. DA-PG cells are autorhythmic and are target of numerous afferents releasing a variety of neurotransmitters, although their properties and role remain elusive. Depolarization induced by Ba2+ blocks spontaneous activity, although the Kir current is not an essential component of the pacemaker machinery. The current is negatively modulated by intracellular cAMP, as shown by a decrease of its amplitude induced by forskolin. Several neuromodulatory effects were tested on the Kir current of DA-PG cell. Activation of metabotropic receptors - known to be present on these cells - shows that the current can be modulated by a multiplicity of pathways. The Kir current can be increased, as observed with agonists of muscarinic, α1 noradrenergic and GABAA receptors, or IKir modulation can caused the opposite effect, i.e. agonists of D2, 5-HT and histamine receptors. These characteristics of the Kir currents provide the basis for additional flexibility of DA-PG cells signaling and function.openFisiologia Sperimentale e ClinicaBorin, MirtaBorin, Mirt

Inward rectifier potassium current in dopaminergic periglomerular cells of mouse olfactory bulb.

Inward rectifier potassium (Kir) channels are important for neuronal signalling and membrane excitability. In this work, patch-clamp techniques were used to characterize Kir channels in mouse dopaminergic (DA) periglomerular (PG) cells. These interneurons are critically placed at the entry of the bulbar circuitry, in contact with terminals of olfactory sensory neurons and with dendrites of projection neurons. Perforated-patch configuration was adopted to record Kir current in DA-PG cells in thin slice. IKir could be distinguished from the hyperpolarization-activated current by showing full activation in < 10 ms, no inactivation, suppression by Ba2+ in a typical voltage-dependent manner and reversal potential nearly coincident with EK. DA-PG cells are autorhythmic and are target of numerous afferents releasing a variety of neurotransmitters, although their properties and role remain elusive. Depolarization induced by Ba2+ blocks spontaneous activity, although the Kir current is not an essential component of the pacemaker machinery. The current is negatively modulated by intracellular cAMP, as shown by a decrease of its amplitude induced by forskolin. Several neuromodulatory effects were tested on the Kir current of DA-PG cell. Activation of metabotropic receptors - known to be present on these cells - shows that the current can be modulated by a multiplicity of pathways. The Kir current can be increased, as observed with agonists of muscarinic, α1 noradrenergic and GABAA receptors, or IKir modulation can caused the opposite effect, i.e. agonists of D2, 5-HT and histamine receptors. These characteristics of the Kir currents provide the basis for additional flexibility of DA-PG cells signaling and function

Pancreatic transdifferentiation and glucose-regulated production of human insulin in the H4IIE rat liver cell line

© 2016 by the authors. Due to the limitations of current treatment regimes, gene therapy is a promising strategy being explored to correct blood glucose concentrations in diabetic patients. In the current study, we used a retroviral vector to deliver either the human insulin gene alone, the rat NeuroD1 gene alone, or the human insulin gene and rat NeuroD1 genes together, to the rat liver cell line, H4IIE, to determine if storage of insulin and pancreatic transdifferentiation occurred. Stable clones were selected and expanded into cell lines: H4IIEins (insulin gene alone), H4IIE/ND (NeuroD1 gene alone), and H4IIEins/ND (insulin and NeuroD1 genes). The H4IIEins cells did not store insulin; however, H4IIE/ND and H4IIEins/ND cells stored 65.5 ± 5.6 and 1475.4 ± 171.8 pmol/insulin/ 5 × 106 cells, respectively. Additionally, several β cell transcription factors and pancreatic hormones were expressed in both H4IIE/ND and H4IIEins/ND cells. Electron microscopy revealed insulin storage vesicles in the H4IIE/ND and H4IIEins/ND cell lines. Regulated secretion of insulin to glucose (0–20 mmol/L) was seen in the H4IIEins/ND cell line. The H4IIEins/ND cells were transplanted into diabetic immunoincompetent mice, resulting in normalization of blood glucose. This data shows that the expression of NeuroD1 and insulin in liver cells may be a useful strategy for inducing islet neogenesis and reversing diabetes