Nobuyuki Koriyama

Involvement of ATP-Sensitive K+ Channels in Free Radical–Mediated Inhibition of Insulin Secretion in Rat Pancreatic β-Cells

To explore the mechanisms of inhibition of insulin secretion in pancreatic β-cells by oxygen free radicals, we studied the effects of H2O2 on membrane currents using the patch-clamp technique. Exposure of β-cells to H2O2 (≥30 (μmol/1) increased the activity of ATP-sensitive potassium (K+ATP) channels without changing the single channel conductance in cell-attached membrane patches. Action currents observed during superfusion of 11.1 mmol/1 glucose were suppressed. In inside-out membrane patches, the activity of K+ATP channels was not influenced by H2O2. In conventional whole-cell clamp experiments using a pipette solution containing 3 mmol/1 ATP, H2O2 did not influence the membrane currents. However, H2O2 did activate the K+ATP channel current in perforated whole-cell clamp configurations. The increased K+ATP channel current was reversed by subsequent exposure to 11.1 mmol/12-ketoisocaproic acid. In cell-attached membrane patches, the K+ATP channel current evoked by exposure to 30 μmol/l H2O2 was inhibited by exposure to 11.1 mmol/l glyceraldehyde, whereas the channel was again activated by exposure to 0.3 mmol/l H2O2. Subsequent superfusion of 11.1 mmol/l 2-ketoisocaproic acid inhibited the channel; this effect was counteracted by exposure to 10 mmol/l H2O2. Transient inhibition of K+ATP channels with provocation of action potentials was observed after washout of 100 μmol/l H2O2 during superfusion of 2.8 or 11.1 mmol/l glucose. We conclude that H2O2 has no direct effect on the K+ATP channels but that it indirectly activates the channels when it is exposed to β-cells under conditions in which the cellular metabolism is physiologically regulated.

Control of catecholamine release and blood pressure with octreotide in a patient with pheochromocytoma: a case report with in vitro studies.

A 65-year-old male patient with pheochromocytoma, whose hypertensive episodes were uncontrolled using conventional therapy, was successfully treated with octreotide (SMS 201-995). The serum catecholamine level and the urinary excretion of catecholamines decreased after 300 μg/day of octreotide was administered. To clarify the mechanisms of octreotide that lower catecholamine released from a tumor, we studied the in vitro effects of octreotide on membrane potentials and voltage-dependent Ca2+ channel (VDCC) current using the whole-cell patch-clamp technique in single pheochromocytoma cells dispersed after tumor resection. The action potentials were reversibly inhibited with 10 μM octreotide. In addition, the VDCC current evoked by depolarized pulses from the holding potential of –60 mV was inhibited with 10 μM octreotide. Octreotide is useful for controlling blood pressure before surgery in some patients with uncontrolled hypertension caused by a pheochromocytoma.

Cyclic AMP/cAMP‐GEF pathway amplifies insulin exocytosis induced by Ca2+ and ATP in rat islet β‐cells

Cyclic AMP (cAMP) plays a pivotal role in insulin secretion induced by incretins. The effects of the second messenger extend to many sites and there has been much controversy on the mechanisms. The aim of this study was to examine how cAMP amplified insulin exocytosis.

Successful treatment of Good syndrome with cytomegalovirus duodenoenteritis using a combination of ganciclovir and immunoglobulin with high anti-cytomegalovirus antibody titer

We describe the case of a 64-year-old woman with Good syndrome who presented with watery diarrhea and abdominal distention caused by cytomegalovirus (CMV) duodenoenteritis. Thymoma and hypogammaglobulinemia were first identified when the patient was 58 years old. She had repeatedly complained of symptoms even after thymectomy. Abdominal radiography revealed multiple air-fluid levels, and computed tomography revealed ascites and dilation of the small intestine. Immunofluorescent staining of specimens obtained by duodenal mucosal biopsy revealed intracellular inclusion bodies of CMV, although serum CMV pp65 antigenemia assays yielded negative results. CMV infection of the small intestine caused mucosal edema resulting in malabsorption. The patient was treated using ganciclovir and an immunoglobulin preparation with a high titer of antibodies against CMV (CMV-Ig), and subsequently made a rapid recovery from abdominal symptoms. When patients with Good syndrome complain of abdominal symptoms, particularly chronic diarrhea, a diagnosis of CMV gastroenteritis should not be excluded, even if negative results are obtained for CMV pp65 antigenemia assays. Combination therapy of ganciclovir and CMV-Ig seems useful for patients with CMV gastroenteritis.

Association of upregulated activity of KATP channels with impaired insulin secretion in UCP1-expressing insulinoma cells

Insulin‐secreting MIN6 cells overexpressing uncoupling protein‐1 (UCP1) were studied regarding insulin secretion in response to various secretagogues. Overexpression of UCP1 prevented an increase of cytosolic ATP levels induced by glucose. In contrast, glucose utilization was not affected, nor was glycerol phosphate flux. The UCP1‐expressing cells showed an inability to increase cytosolic Ca2+ concentration ([Ca2+]i) in response to glucose or α ketoisocaproate and this resulted in less insulin secretion, whereas initial reduction in [Ca2+]i occurring upon either nutrient addition was not affected. Moreover, the effectiveness of tolbutamide on [Ca2+]i increase was reduced and the dose‐response relations for insulin secretion induced by the agent was shifted toward the right in the UCP1‐expressing cells. The resting membrane potential of the UCP1‐expressing cells was significantly hyperpolarized by 6.2 mV compared with control cells. In the perforated and conventional whole‐cell patch‐clamp configurations, the conductance density of ATP‐sensitive K+ (KATP) channels of the UCP1‐expressing cells was 6‐fold and 1.7‐fold greater than that of the control cells, respectively. The sensitivity of KATP channels for tolbutamide was not different between two groups, indicating that in intact cells more than 6‐fold higher concentrations of tolbutamide were required to reduce the KATP channel currents of UCP1‐expressing cells to the same levels as of the control cells. The current density of the voltage‐dependent Ca2+ channels was not influenced. In conclusion, UCP1‐expressing cells showed a refractoriness to respond to tolbutamide as well as nutrients. An upregulated activity of KATP channels was associated with unresponsiveness to the agent in the cells with impaired mitochondrial function.

A case of renal juxtaglomerular cell tumor: usefulness of segmental sampling to prove autonomic secretion of the tumor.

A 27-year-old female patient had been treated for hypertension with conventional therapy for years, because renal vein renin levels failed to show lateralization in renal venous samplings and a renal juxtaglomerular cell tumor (RJGCT) had gone undiagnosed. Abdominal computed tomography revealed a mass at the middle of the right kidney. The right renal venogram demonstrated distinct segmental veins from the upper pole and from the middle and lower poles in the right kidney. On segmental renin sampling from each renal vein, the plasma renin concentration (PRC) of the segmental veins from the middle and lower poles was higher than that from other sites. We diagnosed RJGCT of the right kidney and performed right-sided nephrectomy. After the resection, the PRC rapidly decreased. Immunohistochemical studies using antihuman renin antibodies revealed positive staining of the tumor cells. It is an important strategy to make a segmental sampling at the site as close as possible to the RJGCT.

Heart failure caused by atrial fibrillation in a patient with isolated adrenocorticotropic hormone deficiency and hashimoto's thyroiditis

We report the case of a 75-year-old female patient with a history of Hashimoto′s thyroiditis who presented with congestive heart failure caused by atrial fibrillation associated with isolated adrenocorticotropic hormone (ACTH) deficiency. This is the first case of the combination of these complex conditions. Clinical conditions in a patient with isolated ACTH deficiency and Hashimoto′s thyroiditis can be variable. Thus, it is sometimes difficult to establish a diagnosis. The mechanism underlying heart failure may be complex in some cases. Various conditions can affect patients simultaneously. Therefore, making a proper diagnosis is necessary to improve the patient′s prognosis.