Ca2+ buffering and action potential-evoked Ca2+ signaling in dendrites of pyramidal neurons.
The effect of the fluorescent Ca2+ indicator dye Fura-2 on Ca2+ dynamics was studied in proximal apical dendrites of neocortical layer V and hippocampal CA1 pyramidal neurons in rat brain slices using somatic whole-cell recording and a charge-coupled device camera. A single action potential evoked a transient increase of intradendritic calcium concentration ([Ca2+]i) that was reduced in size and prolonged when the Fura-2 concentration was increased from 20 to 250 microM. Extrapolation to zero Fura-2 concentration suggests that "physiological" transients at 37 degrees C have large amplitudes (150-300 nM) and fast decays (time constant < 100 ms). Assuming a homogeneous compartment model for the dendrite, 0.5-1% of the total Ca2+ entering during an action potential was estimated to remain free. Washout of cytoplasmic Ca2+ buffers was not detectable, suggesting that they are relatively immobile. During trains of action potentials, [Ca2+]i increased and rapidly reached a steady state (time constant < 200 ms), fluctuating around a plateau level which depended linearly on the action potential frequency. Thus, the mean dendritic [Ca2+]i encodes the action potential frequency during physiological patterns of electrical activity and may regulate Ca(2+)-dependent dendritic functions in an activity-dependent way.
Helmchen
F
F
Abteilung Zellphysiologie, Max-Planck-Institut für medizinische Forschung, Heidelberg, Germany.
Imoto
K
K
Sakmann
B
B
D000200:Action Potentials; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002021:Buffers; D002118:Calcium / Q000378:metabolism*; D002451:Cell Compartmentation; D003712:Dendrites / Q000378:metabolism*; D005456:Fluorescent Dyes; D016257:Fura-2; D066298:In Vitro Techniques; D007202:Indicators and Reagents; D007700:Kinetics; D008959:Models, Neurological; D017966:Pyramidal Cells / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction
D002021:Buffers; D005456:Fluorescent Dyes; D007202:Indicators and Reagents; D002118:Calcium; D016257:Fura-2