Cytoplasmic ATP and Ca2+ are implicated in current models of glucose’s control of glucagon and insulin secretion from pancreatic α- and β-cells, respectively, but little is known about ATP and its relation to Ca2+ in α-cells. We therefore expressed the fluorescent ATP biosensor Perceval in mouse pancreatic islets and loaded them with a Ca2+ indicator. With total internal reflection fluorescence microscopy, we recorded subplasma membrane concentrations of Ca2+ and ATP ([Ca2+]pm; [ATP]pm) in superficial α- and β-cells of intact islets and related signaling to glucagon and insulin secretion by immunoassay. Consistent with ATP’s controlling glucagon and insulin secretion during hypo- and hyperglycemia, respectively, the dose-response relationship for glucose-induced [ATP]pm generation was left shifted in α-cells compared to β-cells. Both cell types showed [Ca2+]pm and [ATP]pm oscillations in opposite phase, probably reflecting energy-consuming Ca2+ transport. Although pulsatile insulin and glucagon release are in opposite phase, [Ca2+]pm synchronized in the same phase between α- and β-cells. This paradox can be explained by the overriding of Ca2+ stimulation by paracrine inhibition, because somatostatin receptor blockade potently stimulated glucagon release with little effect on Ca2+. The data indicate that an α-cell-intrinsic mechanism controls glucagon in hypoglycemia and that paracrine factors shape pulsatile secretion in hyperglycemia.—Li, J., Yu, Q., Ahooghalandari, P., Gribble, F. M., Reimann, F., Tengholm, A., Gylfe, E. Submembrane ATP and Ca2+ kinetics in α-cells: unexpected signaling for glucagon secretion.

Aims/hypothesis Glucagon is critical for normal glucose homeostasis and aberrant secretion of the hormone aggravates dysregulated glucose control in diabetes. However, the mechanisms by which glucose controls glucagon secretion from pancreatic alpha cells remain elusive. The aim of this study was to investigate the role of the intracellular messenger cAMP in alpha-cell-intrinsic glucose regulation of glucagon release. Methods Subplasmalemmal cAMP and Ca 2+ concentrations were recorded in isolated and islet-located alpha cells using fluorescent reporters and total internal reflection microscopy. Glucagon secretion from mouse islets was measured using ELISA. Results Glucose induced Ca 2+ -independent alterations of the subplasmalemmal cAMP concentration in alpha cells that correlated with changes in glucagon release. Glucose-lowering-induced stimulation of glucagon secretion thus corresponded to an elevation in cAMP that was independent of paracrine signalling from insulin or somatostatin. Imposed cAMP elevations stimulated glucagon secretion and abolished inhibition by glucose elevation, while protein kinase A inhibition mimicked glucose suppression of glucagon release. Conclusions/interpretation Glucose concentrations in the hypoglycaemic range control glucagon secretion by directly modulating the cAMP concentration in alpha cells independently of paracrine influences. These findings define a novel mechanism for glucose regulation of glucagon release that underlies recovery from hypoglycaemia and may be disturbed in diabetes. Electronic supplementary material The online version of this article (10.1007/s00125-019-4857-6) contains peer-reviewed but unedited supplementary material, which is available to authorised users.

Bovine respiratory syncytial virus (BRSV) is a major cause of bronchiolitis and pneumonia in cattle and causes yearly outbreaks with high morbidity in Europe. Commercial vaccines against this virus needs improvement of efficacy, especially in calves with BRSV-specific maternally derived antibodies (MDA). We previously reported that an experimental BRSV-ISCOM vaccine, but not a commercial vaccine, induced strong clinical and virological protection in calves with MDA, immunized at 7-15 weeks of age. The aim of the present study was to characterize the immune responses, as well as to investigate the efficacy and safety in younger animals, representing the target population for vaccination. Four groups of five 3-8 week old calves with variable levels of BRSV-specific MDA were immunized s.c. twice at a 3 weeks interval with (i) BRSV immunostimulating complexes (BRSV-ISCOMs), (ii) BRSV-protein, (iii) adjuvant, or (iv) PBS. All calves were challenged with virulent BRSV by aerosol 2 weeks later and euthanized on day 6 after infection. The cellular and humoral responses were monitored as well as the clinical signs, the viral excretion and the pathology following challenge. Despite presence of MDA at the time of the immunization, only a minimum of clinical signs were observed in the BRSV-ISCOM group after challenge. In contrast, in all control groups, clinical signs of disease were observed in most of the animals (respiratory rates up to 76min(-1) and rectal temperatures up to 41°C). The clinical protection was associated to a highly significant reduction of virus replication in the upper and lower respiratory tract of calves, rapid systemic and local antibody responses and T helper cell responses dominated by IFNγ production. Animals that did not shed virus detectable by PCR or cell culture following challenge possessed particularly high levels of pulmonary IgA. The protective immunological responses to BRSV proteins and the ability to overcome the inhibiting effect of MDA were dependent on ISCOM borne antigen presentation.

Serine proteases are the major protein constituents within mast cell secretory granules. These proteases are subdivided into chymases and tryptases depending on their primary cleavage specificity. Here, we present the extended cleavage specificity of the macaque mast cell chymase and compare the specificity with human chymase (HC) and dog chymase (DC) that were produced in the same insect cell expression host. The macaque chymase (MC) shows almost identical characteristics as the HC, including both primary and extended cleavage specificities as well as sensitivity to protease inhibitors, whereas the DC differs in several of these characteristics. Although previous studies have shown that mouse mast cell protease-4 (mMCP-4) is similar in its hydrolytic specificity to the HC, mouse mast cells contain several related enzymes. Thus mice may not be the most appropriate model organism for studying HC activity and inhibition. Importantly, macaques express only one chymase and, as primates, are closely related to human general physiology. In addition, the human and macaque enzymes both cleave angiotensin I (Ang I) in the same way, generating primarily angiotensin II (Ang II) and they do not further degrade the peptide like most rodent enzymes do. Both enzymes also cleave two additional potential in vivo substrates, fibronectin and secretory leukocyte protease inhibitor (SLPI) in a similar way. Given the fact that both HC and MC are encoded by a single gene with high sequence homology and that many physiological processes are similar between these species, the macaque may be a very interesting model to study the physiological role of the chymase and to determine the potency and potential side-effects of various chymase inhibitors designed for therapeutic human use.

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