Electron microscopy and quantitative stereological techniques were used to study the dynamics of the docked granule pool in the rat pancreatic -cell. The mean number of granules per -cell was 11,136. After equilibration in RPMI containing 5.6 mmol/l glucose, 6.4% of the granules (ϳ700) were docked at the plasma membrane (also measured as [means ؎ SE] 4.3 ؎ 0.6 docked granules per 10 m of plasma membrane at the perimeter of the cell sections). After a 40-min exposure to 16.7 mmol/l glucose, 10.2% of the granules (ϳ1,060) were docked (6.4 ؎ 0.8 granules per 10 m of plasma membrane). Thus, the docked pool increased by 50% during stimulation with glucose. Islets were also exposed to 16.7 mmol/l glucose in the absence or presence of 10 mol/l nitrendipine. In the absence and presence of nitrendipine, there were 6.1 ؎ 0.7 and 6.3 ؎ 0.6 granules per 10 m of membrane, respectively. Thus, glucose increased granule docking independently of increased [Ca 2؉ ]i and exocytosis. The data suggest a limit to the number of docking sites. As the rate of docking exceeded the rate of exocytosis, docking is not rate limiting for insulin release. Only with extremely high release rates, glucose stimulation after a 4-h incubation with a high concentration of fatty acid-free BSA, was the docked granule pool reduced in size. Diabetes 53:3179 -3183, 2004 I n glucose-stimulated biphasic insulin secretion, the first phase is due to the ATP-sensitive K ϩ channeldependent pathway of glucose signaling, depolarization of the cell, increased Ca 2ϩ influx, and exocytosis of an "immediately releasable" pool of docked granules (1-4). After the first phase, in rat and human, the second phase is characterized by an increasing rate of secretion to a plateau. It has been suggested that the second phase is due to time-dependent potentiating signals (5-7) generated by the ATP-sensitive K ϩ channelindependent or -amplifying pathway (7). The mechanisms underlying this pathway and the second phase of release are unknown (1,7-9), although it has been suggested that its action is at the level of the docked granules to increase the rate at which they enter the immediately releasable pool or state (7). Second-phase secretion over a lengthy period requires that the -cell replace the released docked granules. For this to happen, a flow of granules from the large reserve pool to the plasma membrane followed by docking and subsequent priming and preparation for release has to occur. Little is known about this movement or about the dynamics of the docked granules. The aim of this research was to determine whether the increased rate of insulin secretion during the second phase was associated with any change in the number of granules docked at the -cell plasma membrane.
RESEARCH DESIGN AND METHODSMale Sprague-Dawley rats weighing 250 -350 g were used for the study and fed ad libitum. They were killed by CO 2 asphyxiation and the pancreata removed. Pancreatic islets were isolated by collagenase digestion (10), as previously described using a Krebs-Ringer bicarbonate...
BackgroundShortening tuberculosis (TB) treatment duration is a research priority. This paper presents data from a prematurely terminated randomized clinical trial, of 4-month moxifloxacin or gatifloxacin regimens, in South India.MethodsNewly diagnosed, sputum-positive HIV-negative pulmonary TB patients were randomly allocated to receive gatifloxacin or moxifloxacin, along with isoniazid and rifampicin for 4 months with pyrazinamide for first 2 months (G or M) or isoniazid and rifampicin for 6 months with ethambutol and pyrazinamide for first 2 months (C). All regimens were administered thrice-weekly. Clinical and bacteriological assessments were done monthly during treatment and for 24 months post-treatment. The Data and Safety Monitoring Board recommended termination of the trial due to high TB recurrence rates in the G and M regimens.ResultsOf 416 patients in intent-to-treat analysis, 6 (5%) of 124, 2 (2%) of 110 and 2 (2%) of 137 patients with drug-susceptible TB in the G, M and C arms respectively had unfavorable response at the end of treatment; during the next 24 months, 17 (15%) of 115, 11 (11%) of 104 and 8 (6%) of 132 patients respectively, had TB recurrence. Of 38 drug-resistant patients 1 of 8 and 3 of 26 in the G and C arms respectively had unfavourable response at the end of treatment; and TB recurrence occurred in 2 of 7 and 2 of 23 patients, respectively. The differences in TB recurrence rates between the G and C arms was statistically significant (p = 0.02). Gastro-intestinal symptoms occurred in 23%, 22% and 9% of patients in the G, M and C arms respectively, but most reactions were mild and manageable with symptomatic measures; 1% required regimen modification.Conclusions4-month thrice-weekly regimens of gatifloxacin or moxifloxacin with isoniazid, rifampicin and pyrazinamide, were inferior to standard 6-month treatment, in patients with newly diagnosed sputum positive pulmonary TB.Trial RegistrationClinical Trials Registry of India CTRI/2012/10/003060
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