Changes in free calcium ion concentration recorded inside hippocampal pyramidal cells in situ.
In rats under urethane or pentobarbitone anesthesia, Ca2+ -sensitive microelectrodes were inserted into CA3 and CA1 hippocampal cells. In 23 neurons with a mean resting membrane potential (Vm) of -56.9 mV, the Ca potential (VCa) fell below Vm by an average of -22.1 mV (S.D. +/- 19.1 mV), indicating a mean intracellular free Ca2+ concentration ([Ca]i) of 9.7 microM (S.D. 14.9 microM). In spite of their better and more stable Vm (mean -67.1 mV), unresponsive cells (probably neuroglia) had a higher and more variable [Ca]i (mean 37.0 +/- 51.2 microM). In 21 of the neurons, repetitive stimulation of the fimbria--at 5-20 Hz for 30s, which is sufficient to elicit bursts of population spikes--evoked substantial increases in [Ca]i: the mean increase observed during or just after 29 such tetani was +27.1 +/- 54.5 microM. Typically [Ca]i reached a peak near the end of the tetanus and then decayed with a half-time of 5-10 s, though not necessarily to the initial level. In 7 cells, a large increase in [Ca] (mean +239 +/- 367 microM) appeared as a late event, 20-30 s after the end of the tetanus. In 5 cells, [Ca]i could thus be raised transiently to 10(-4) M or higher. All these increases in [Ca]i are far greater than can be evoked by tetanic activation in spinal motoneurons; their possible significance for long term potentiation or cell necrosis in the hippocampus is discussed.
D000818:Animals; D001826:Body Fluids / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002452:Cell Count; D004558:Electric Stimulation; D005071:Evoked Potentials; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D007424:Intracellular Fluid / Q000378:metabolism*; D009457:Neuroglia / Q000378:metabolism / Q000502:physiology; D009474:Neurons / Q000378:metabolism* / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000502:physiology
D002118:Calcium