Characteristics and functions of {alpha}-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors expressed in mouse pancreatic {alpha}-cells.
Pancreatic islet cells use neurotransmitters such as l-glutamate to regulate hormone secretion. We determined which cell types in mouse pancreatic islets express ionotropic glutamate receptor channels (iGluRs) and describe the detailed biophysical properties and physiological roles of these receptors. Currents through iGluRs and the resulting membrane depolarization were measured with patch-clamp methods. Ca(2+) influx through voltage-gated Ca(2+) channels and Ca(2+)-evoked exocytosis were detected by Ca(2+) imaging and carbon-fiber microamperometry. Whereas iGluR2 glutamate receptor immunoreactivity was detected using specific antibodies in immunocytochemically identified mouse alpha- and beta-cells, functional iGluRs were detected only in the alpha-cells. Fast application of l-glutamate to cells elicited rapidly activating and desensitizing inward currents at -60 mV. By functional criteria, the currents were identified as alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors. They were activated and desensitized by AMPA, and were activated only weakly by kainate. The desensitization by AMPA was inhibited by cyclothiazide, and the currents were blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Islet iGluRs showed nonselective cation permeability with a low Ca(2+) permeability (P(Ca)/P(Na) = 0.16). Activation of the AMPA receptors induced a sequence of cellular actions in alpha-cells: 1) depolarization of the membrane by 27 +/- 3 mV, 2) rise in intracellular Ca(2+) mainly mediated by voltage-gated Ca(2+) channels activated during the membrane depolarization, and 3) increase of exocytosis by the Ca(2+) rise. In conclusion, iGluRs expressed in mouse alpha-cells resemble the low Ca(2+)-permeable AMPA receptor in brain and can stimulate exocytosis.
Cho
Jung-Hwa
JH
Department of Physiology and Biophysics, University of Washington School of Medicine, G-424 Health Science Building, Box 357290, Seattle, Washington 98195-7290, USA.
Chen
Liangyi
L
Kim
Mean-Hwan
MH
Chow
Robert H
RH
Hille
Bertil
B
Koh
Duk-Su
DS
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D015220:Calcium Channels / Q000502:physiology; D048429:Cell Size; D004594:Electrophysiology; D018690:Excitatory Amino Acid Agonists / Q000378:metabolism / Q000494:pharmacology; D005089:Exocytosis / Q000502:physiology; D005934:Glucagon / Q000235:genetics / Q000378:metabolism; D050416:Glucagon-Secreting Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D018698:Glutamic Acid / Q000494:pharmacology / Q000502:physiology*; D007150:Immunohistochemistry; D007328:Insulin / Q000235:genetics / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D007608:Kainic Acid / Q000378:metabolism / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018091:Receptors, AMPA / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000378:metabolism / Q000494:pharmacology
D015220:Calcium Channels; D018690:Excitatory Amino Acid Agonists; D007328:Insulin; D012333:RNA, Messenger; D018091:Receptors, AMPA; D018698:Glutamic Acid; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D005934:Glucagon; D007608:Kainic Acid