L-glutamate suppresses HVA calcium current in catfish horizontal cells by raising intracellular proton concentration.
Catfish horizontal cells exhibit a high voltage-activated, slowly inactivating calcium (HVA) current. In isolated cells, this current underlies a sustained action potential that can be evoked by depolarization. L-Glutamate at concentrations as low as 1 microM suppressed HVA current and shortened the duration of action potentials. pH indicator dye measurements revealed that L-glutamate acidified cells by up to 0.3 pH units. pH/HVA current dose-response curves indicated that the EC50 for pH inhibition of HVA current was 7.1 and the Hill coefficient was 1.98. L-Glutamate's suppression of HVA current was eliminated when the patch pipette solution contained a high concentration of proton buffer, but was not affected when pipettes contained GTP gamma S. These results support the hypothesis that L-glutamate can modulate HVA current by changing intracellular pH.
Dixon
D B
DB
Department of Ophthalmology, University of California, San Francisco 94143-0730.
Takahashi
K
K
Copenhagen
D R
DR
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002021:Buffers; D002118:Calcium / Q000502:physiology*; D002397:Catfishes; D004594:Electrophysiology; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism*; D009994:Osmolar Concentration; D011522:Protons; D012160:Retina / Q000166:cytology / Q000502:physiology*
D002021:Buffers; D005971:Glutamates; D011522:Protons; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D018698:Glutamic Acid; D002118:Calcium