A novel glutamate-mediated inhibitory mechanism linked with Ca2+/calmodulin-dependent protein kinase II in identified Euhadra neurons.
The underlying mechanism(s) of the glutamate (Glu)-induced membrane hyperpolarizing response in identified Euhadra neurons was investigated using the voltage-clamp technique, pressure injection method, and pharmacologic agents. Under voltage-clamp conditions, bath-applied Glu elicits a slow outward potassium current (Glu current) accompanied by an increase in membrane conductance whose amplitude is dose dependent. Of the agonists tested, the Glu current was mimicked only by quisqualate (QA); its potency was approximately 10 times greater than that of Glu. Typical antagonists for the ionotropic type of Glu receptors and G protein inhibitors do not block this current. The Glu current is markedly enhanced by a specific inhibitor of Ca2+/ calmodulin-dependent protein kinase II (CaM-KII), KN-62 (1-[N,O-bis (1,5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine) in a dose-dependent manner, while intracellularly injected CaM-KII suppresses the current. The potent protein kinase A inhibitors, H-8 (N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride) and H-89 (N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide) or the specific protein kinase C inhibitors staurosporine and K-252b had no effect on the Glu current. These results suggest the presence of a novel subtype of Glu receptor in Euhadra neurons, which may be coupled to the activation of potassium channels normally suppressed by CaM-KII.
Watanabe
K
K
Department of Physiology, Gifu University School of Medicine, Japan.
Yamamoto
T
T
Ozono
S
S
Nagasaki
S
S
Onozuka
M
M
D000818:Animals; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D018698:Glutamic Acid / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects*; D012908:Snails
D018698:Glutamic Acid; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases