Metabotropic glutamate receptor activation enhances the activities of two types of Ca2+-activated k+ channels in rat hippocampal astrocytes.
The influence of activation of glutamate receptor (GluR) on outward K(+) current in cultured neonate rat hippocampal astrocytes was investigated. Patch-clamp analysis of K(+) channel currents in cultured astrocytes identified the existence of 71 +/- 6 and 161 +/- 11 pS single-channel K(+) currents that were sensitive to changes in voltage and [Ca(2+)](i) and blocked by external TEA but not by charybdotoxin, iberiotoxin, apamin, or 4-aminopyridine. Reverse transcriptase (RT)-PCR and Northern blot analysis revealed transcripts of the Ca(2+)-activated K(+) channel (K(Ca)) beta(4)-subunit (beta4) (KCNMB4) in cultured astrocytes. Expression of the metabotropic glutamate receptor (mGluR) subtypes mGluR1 and mGluR5 and the ionotropic glutamate receptor (iGluR) subtypes iGluR1 and iGluR4 were detected by RT-PCR and immunofluorescence analysis in cultured astrocytes. The mGluR agonists L-glutamate and quisqualate increased the open state probability (NP(o)) of the 71 and 161 pS K(+) channel currents that were prevented by the mGluR receptor antagonists 1-aminoindan-1,5-dicarboxylic acid or L-(+)-2-amino-3-phosphonopropionic acid and not by the iGluR antagonists (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine maleate or CNQX. Activation of the two types of K(+) channel currents by mGluR agonists was attenuated by pertussis toxin and by inhibition of phospholipase C (PLC) or cytochrome P450 arachidonate epoxygenase. These results indicate that brain astrocytes contain the KCNMB4 transcript and express two novel types of K(Ca) channels that are gated by activation of a G-protein coupled metabotropic glutamate receptor functionally linked to PLC and cytochrome P450 arachidonate epoxygenase activity.
Gebremedhin
Debebe
D
Department of Physiology and Cardiovascular Research Center, Medical College of Wisconsin, Milwaukee 53226, USA. mariyei@mcw.edu
Yamaura
Ken
K
Zhang
Chenyang
C
Bylund
Johan
J
Koehler
Raymond C
RC
Harder
David R
DR
D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002478:Cells, Cultured; D000090762:Cytochrome P-450 CYP2J2; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology; D051038:Large-Conductance Calcium-Activated Potassium Channel beta Subunits; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D010105:Oxygenases / Q000037:antagonists & inhibitors; D018408:Patch-Clamp Techniques; D037342:Pertussis Toxin / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism; D024681:Potassium Channels, Calcium-Activated / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018094:Receptors, Metabotropic Glutamate / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; C485821:Kcnmb4 protein, rat; D051038:Large-Conductance Calcium-Activated Potassium Channel beta Subunits; D009419:Nerve Tissue Proteins; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D018094:Receptors, Metabotropic Glutamate; D003577:Cytochrome P-450 Enzyme System; D010105:Oxygenases; D000090762:Cytochrome P-450 CYP2J2; D037342:Pertussis Toxin; D010738:Type C Phospholipases; D011188:Potassium; D002118:Calcium