Peter Thams1, Mohammad R Anwar, Kirsten Capito. 1. Department of Medical Biochemistry and Genetics, The Panum Institute, University of Copenhagen, Denmark. thams@imbg.ku.dk
Abstract
OBJECTIVE: To assess the significance of protein kinase A (PKA) in glucose triggering of ATP-sensitive K(+) (K(+)(ATP)) channel-dependent insulin secretion and in glucose amplification of K(+)(ATP) channel-independent insulin secretion. METHODS: Insulin release from cultured perifused mouse pancreatic islets was determined by radioimmunoassay. RESULTS: In islets cultured at 5.5 mmol/l glucose, and then perifused in physiological Krebs-Ringer medium, the PKA inhibitors, H89 (10 micromol/l) and PKI 6-22 amide (30 micromol/l) did not inhibit glucose (16.7 mmol/l)-induced insulin secretion, but inhibited stimulation by the adenylyl cyclase activator, forskolin (10 micromol/l). In the presence of 60 mmol/l K(+) and 250 micromol/l diazoxide, which stimulates maximum Ca(2+) influx independently of K(+)(ATP) channels, H89 (10 micromol/l) inhibited Ca(2+)-evoked insulin secretion, but failed to prevent glucose amplification of K(+)(ATP) channel-independent insulin secretion. In the presence of 1 mmol/l ouabain and 250 micromol/l diazoxide, which cause modest Ca(2+) influx, glucose amplification of K(+)(ATP) channel-independent insulin secretion was observed without concomitant Ca(2+) stimulation of PKA activity. In islets cultured at 16.7 mmol/l glucose, glucose (16.7 mmol/l)-induced insulin secretion in physiological Krebs-Ringer medium was augmented and now inhibited by H89 (10 micromol/l), implicating that culture at 16.7 mmol/l glucose may increase Ca(2+)-sensitive adenylyl cyclase activity and hence PKA activity. In accordance, Ca(2+)-evoked insulin secretion at 60 mmol/l K(+) and 250 micromol/l diazoxide was improved, whereas glucose amplification of K(+)(ATP) channel-independent insulin secretion was unaffected. CONCLUSIONS: Glucose may activate PKA through triggering of the K(+)(ATP) channel-dependent pathway. Glucose amplification of K(+)(ATP) channel-independent insulin secretion, on the other hand, occurs by PKA-independent mechanisms.
OBJECTIVE: To assess the significance of protein kinase A (PKA) in glucose triggering of ATP-sensitive K(+) (K(+)(ATP)) channel-dependent insulin secretion and in glucose amplification of K(+)(ATP) channel-independent insulin secretion. METHODS: Insulin release from cultured perifused mousepancreatic islets was determined by radioimmunoassay. RESULTS: In islets cultured at 5.5 mmol/l glucose, and then perifused in physiological Krebs-Ringer medium, the PKA inhibitors, H89 (10 micromol/l) and PKI 6-22 amide (30 micromol/l) did not inhibit glucose (16.7 mmol/l)-induced insulin secretion, but inhibited stimulation by the adenylyl cyclase activator, forskolin (10 micromol/l). In the presence of 60 mmol/l K(+) and 250 micromol/l diazoxide, which stimulates maximum Ca(2+) influx independently of K(+)(ATP) channels, H89 (10 micromol/l) inhibited Ca(2+)-evoked insulin secretion, but failed to prevent glucose amplification of K(+)(ATP) channel-independent insulin secretion. In the presence of 1 mmol/l ouabain and 250 micromol/l diazoxide, which cause modest Ca(2+) influx, glucose amplification of K(+)(ATP) channel-independent insulin secretion was observed without concomitant Ca(2+) stimulation of PKA activity. In islets cultured at 16.7 mmol/l glucose, glucose (16.7 mmol/l)-induced insulin secretion in physiological Krebs-Ringer medium was augmented and now inhibited by H89 (10 micromol/l), implicating that culture at 16.7 mmol/l glucose may increase Ca(2+)-sensitive adenylyl cyclase activity and hence PKA activity. In accordance, Ca(2+)-evoked insulin secretion at 60 mmol/l K(+) and 250 micromol/l diazoxide was improved, whereas glucose amplification of K(+)(ATP) channel-independent insulin secretion was unaffected. CONCLUSIONS:Glucose may activate PKA through triggering of the K(+)(ATP) channel-dependent pathway. Glucose amplification of K(+)(ATP) channel-independent insulin secretion, on the other hand, occurs by PKA-independent mechanisms.
Authors: Grant G Kelley; Oleg G Chepurny; Frank Schwede; Hans-G Genieser; Colin A Leech; Michael W Roe; Xiangquan Li; Igor Dzhura; Elvira Dzhura; Parisa Afshari; George G Holz Journal: Islets Date: 2009 Nov-Dec Impact factor: 2.694
Authors: Igor Dzhura; Oleg G Chepurny; Grant G Kelley; Colin A Leech; Michael W Roe; Elvira Dzhura; Parisa Afshari; Sundeep Malik; Michael J Rindler; Xin Xu; Youming Lu; Alan V Smrcka; George G Holz Journal: J Physiol Date: 2010-11-01 Impact factor: 5.182
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