Suppression of a Ca2+ current by NMDA and intracellular Ca2+ in acutely isolated hippocampal neurons.
1. Ca2+ current was examined in acutely isolated hippocampal cells with the use of whole cell voltage-clamp recording and under continuous intracellular perfusion. A persistent Ca2+ current was activated by depolarization to -10 mV from a holding potential of -50 mV. 2. The persistent Ca2+ current was suppressed upon a wash out of the intracellular Mg(2+)-ATP. Adenosine 3',5'-cyclic monophosphate (cAMP) introduced intracellularly potentiated the Ca2+ current, and kinase A inhibitor blocked the current. 3. Reversible suppression of the persistent Ca2+ current was also observed by elevating intracellular Ca2+. This Ca(2+)-dependent suppression was retarded by the addition of a phosphatase inhibitor, okadaic acid, to the intracellular solution. 4. N-methyl-D-aspartate (NMDA) elicited inward current (NMDA response) in the isolated cells. The persistent Ca2+ current was transiently suppressed after the NMDA response. Suppression of the Ca2+ current by NMDA was reduced when intracellular Ca2+ buffering capacity was increased by increasing the concentration of bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA) from a concentration of 1-10 mM. 5. Substitution of ATP in the intracellular solution with ATP-gamma-S or the addition of okadaic acid to the intracellular solution reduced the suppressive effect of NMDA on the Ca2+ current. 6. The results suggest that the persistent Ca2+ current in the hippocampal cells is maintained by a kinase A-mediated phosphorylation. Increases in the intracellular Ca2+ concentration suppressed the Ca2+ current via a mechanism involving a phosphatase. Ca2+ entry through the NMDA receptor channel suppressed the Ca2+ channel by activating the phosphatase.
Chen
Q X
QX
Department of Pharmacology, State University of New York, Brooklyn 11203, USA.
Wong
R K
RK
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology*; D002469:Cell Separation; D004553:Electric Conductivity; D006168:Guinea Pigs; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D007425:Intracellular Membranes / Q000378:metabolism*; D016202:N-Methylaspartate / Q000494:pharmacology*; D009474:Neurons / Q000502:physiology*; D010766:Phosphorylation; D010770:Phosphotransferases / Q000502:physiology
D016202:N-Methylaspartate; D000255:Adenosine Triphosphate; D010770:Phosphotransferases; D002118:Calcium