]c was elevated and controlled by KCl or tolbutamide, the amplifying action of glucose was facilitated by actin depolymerization and unaffected by polymerization. Both phases of IS were larger in response to high-glucose than to tolbutamide in low-glucose, although triggering [Ca 2ϩ ]c was lower. This difference in IS, due to amplification, persisted when the IS rate was doubled by actin depolymerization or polymerization. In conclusion, metabolic amplification is rapid and influences the first as well as the second phase of IS. It is a late step of stimulus-secretion coupling, which does not require functional actin microfilaments and could correspond to acceleration of the priming process conferring release competence to insulin granules. biphasic insulin release; cytosolic calcium; exocytosis; insulin granules; pancreatic islets THE RATE OF INSULIN SECRETION by pancreatic ␤-cells is controlled by a hierarchical interaction among circulating nutrients, hormones, and neurotransmitters. The preeminent influence of glucose itself is exerted via two signaling pathways that both require metabolism of the sugar in ␤-cells (1, 11, 39). In the triggering pathway, closure of ATP-sensitive potassium (K ATP ) channels by adenine nucleotides permits membrane depolarization, which leads to Ca 2ϩ influx through voltagegated calcium channels and results in an increase in the cytosolic free Ca 2ϩ concentration ([Ca 2ϩ ] c ) that eventually triggers exocytosis of insulin granules. Simultaneously, glucose activates a metabolic amplifying pathway that does not involve additional action on K ATP channels or further rise in [Ca 2ϩ ] c but that augments the secretory response to the triggering Ca 2ϩ signal (14). The cellular mechanisms and effectors of this amplification have not yet been identified.During a hyperglycemic clamp, the increase in plasma insulin concentration is biphasic in humans (4) and rodents (13,29). In vitro, when a perfused pancreas or perifused isolated islets are challenged by an abrupt and steady increase in the glucose concentration, the acceleration of insulin secretion follows a biphasic pattern with a prominent rapid first phase and a sustained second phase (6,12,13,39,54). The mechanisms underlying the biphasic kinetics of insulin secretion are incompletely elucidated and probably involve both the time course of intracellular signals and the distribution of insulin granules in distinct pools (12,27,30,35,41,50). The first phase is commonly attributed to Ca 2ϩ -induced exocytosis of insulin granules from a limited pool of docked (tethered to the plasma membrane) and primed (release competent) granules. In contrast, the second phase is thought to involve functional recruitment or physical translocation of granules to the exocytotic sites. The characteristics and localization of this or these reserve pool(s) are still disputed (3,16,19,31,35,38). However, the general view holds that the amplifying action of glucose is necessary for the second phase but not involved in the first phase.Most actin micro...

The aims of this study were to determine the most optimal timing to start machine perfusion during kidney preservation to improve early graft function and to evaluate the impact of temperature and oxygen supply during machine perfusion in a porcine ischemia-reperfusion autotransplant model. The left kidney of an approximately 40-kg female Belgian Landrace pig was exposed to 30 minutes of warm ischemia via vascular clamping and randomized to 1 of 6 study groups: (1) 22-hour static cold storage (SCS) (n = 6), (2) 22-hour hypothermic machine perfusion (HMP) (n = 6), (3) 22-hour oxygenated HMP (n = 7), (4) 20-hour HMP plus 2-hour normothermic perfusion (NP) (n = 6), (5) 20-hour SCS plus 2-hour oxygenated HMP (n = 7), and (6) 20-hour SCS plus 2-hour NP (n = 6). Graft recovery measured by serum creatinine level was significantly faster for continuous HMP preservation strategies compared with SCS alone and for all end-ischemic strategies. The active oxygenated 22-hour HMP group demonstrated a significantly faster recovery from early graft function compared with the 22-hour nonactive oxygenated HMP group. Active oxygenation was also found to be an important modulator of a faster increase in renal flow during HMP preservation. Continuous oxygenated HMP applied from the time of kidney procurement until transplant might be the best preservation strategy to improve early graft function.

At the 2015 combined congress of the CTS, IPITA, and IXA, a symposium was held to discuss recent progress in pig islet xenotransplantation. The presentations focused on 5 major topics – (i) the results of 2 recent clinical trials of encapsulated pig islet transplantation, (ii) the inflammatory response to encapsulated pig islets, (iii) methods to improve the secretion of insulin by pig islets, (iv) genetic modifications to the islet-source pigs aimed to protect the islets from the primate immune and/or inflammatory responses, and (v) regulatory aspects of clinical pig islet xenotransplantation. Trials of microencapsulated porcine islet transplantation to treat unstable type 1 diabetic patients have been associated with encouraging preliminary results. Further advances to improve efficacy may include (i) transplantation into a site other than the peritoneal cavity, which might result in better access to blood, oxygen, and nutrients; (ii) the development of a more biocompatible capsule and/or the minimization of a foreign body reaction; (iii) pig genetic modification to induce a greater secretion of insulin by the islets, and/or to reduce the immune response to islets released from damaged capsules; and (iv) reduction of the inflammatory response to the capsules/islets by improvements in the structure of the capsules and/or in genetic-engineering of the pigs and/or in some form of drug therapy. Ethical and regulatory frameworks for islet xenotransplantation are already available in several countries, and there is now a wider international perception of the importance of developing an internationally-harmonized ethical and regulatory framework.