A novel D-phenylalanine-derivative hypoglycemic agent A-4166 increases cytosolic free Ca2+ in rat pancreatic beta-cells by stimulating Ca2+ influx.
It has recently been shown that N-[(trans-4-isopropylcyclohexyl)-carbonyl]D-phenylalanine (A-4166), a new nonsulfonylurea oral hypoglycemic agent, reduces blood glucose levels in nondiabetic and diabetic animals in a quicker and shorter lasting manner than sulfonylureas, and that the hypoglycemic effect of A-4166 is due to the stimulation of insulin release. However, the mechanism by which A-4166 stimulates insulin release is still unknown. In the present study, we investigated the effect of A-4166 on the cytosolic free Ca2+ concentration ([Ca2+]i) in pancreatic beta-cells from normal rats by dual wavelength fura-2 microfluorometry. In the presence of 2.8 mM glucose, A-4166 produced a rapid increase in [Ca2+]i in a concentration-dependent manner over the range of 3-30 microM. The increase in [Ca2+]i was transient, oscillatory, or sustained. A-4166 did not evoke any decrease in [Ca2+]i, whereas a high concentration of glucose (16.7 mM), a metabolized secretagogue, produced an initial decrease and a subsequent increase in [Ca2+]i. In the presence of 16.7 mM glucose, low concentrations (0.03-1 microM) of A-4166 produced an increase in [Ca2+]i in some of the beta-cells tested. The [Ca2+]i response to A-4166 was completely and reversibly inhibited under Ca(2+)-free conditions as well as by nitrendipine, a blocker of the L-type Ca2+ channel. Nitrendipine also inhibited insulin release from perfused rat pancreases stimulated by A-4166. Diazoxide, an opener of the ATP-sensitive K+ channel, blocked the [Ca2+]i response to A-4166. Sulfonylureas such as tolbutamide and glibenclamide increased [Ca2+]i in a manner similar to A-4166. These results indicate that at basal glucose concentrations, A-4166 increases [Ca2+]i in rat pancreatic beta-cells by stimulating Ca2+ influx through L-type Ca2+ channels, and that this effect is markedly augmented at elevated glucose concentrations. It appears that the increase in [Ca2+]i is related to the stimulation of insulin release by A-4166. Inhibition of ATP-sensitive potassium channels, but not stimulation of beta-cell metabolism, may be involved in the increase in [Ca2+]i by A-4166.
Fujitani
S
S
Department of Physiology, Kagoshima University School of Medicine, Japan.
Yada
T
T
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003510:Cyclohexanes / Q000494:pharmacology*; D003600:Cytosol / Q000378:metabolism; D003981:Diazoxide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000494:pharmacology; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007515:Islets of Langerhans / Q000187:drug effects* / Q000378:metabolism; D000077715:Nateglinide; D009568:Nitrendipine / Q000494:pharmacology; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D013453:Sulfonylurea Compounds / Q000494:pharmacology
D003510:Cyclohexanes; D007004:Hypoglycemic Agents; D015221:Potassium Channels; D013453:Sulfonylurea Compounds; D000077715:Nateglinide; D010649:Phenylalanine; D009568:Nitrendipine; D005947:Glucose; D003981:Diazoxide; D002118:Calcium