Calcium signaling in a narrow somatic submembrane shell during synaptic activity in cerebellar Purkinje neurons.
Temporal and spatial changes in the intracellular Ca2+ concentration ([Ca2+]i) were examined in dendrites and somata of rat cerebellar Purkinje neurons by combining whole-cell patch-clamp recording and fast confocal laser-scanning microscopy. In cells loaded via the patch pipette with the high-affinity Ca2+ indicator Calcium Green-1 (Kd approximately 220 nM), a single synaptic climbing fiber response, a so-called complex spike, resulted in a transient elevation of [Ca2+]i that showed distinct differences among various subcellular compartments. With conventional imaging, the Ca2+ signals were prominent in the dendrites and almost absent in the soma. Confocal recordings from the somatic region, however, revealed steep transient increases in [Ca2+]i that were confined to a submembrane shell of 2- to 3-microns thickness. In the central parts of the soma [Ca2+]i increases were much slower and had smaller amplitudes. The kinetics and amplitudes of the changes in [Ca2+]i were analyzed in more detail by using the fast, low-affinity Ca2+ indicator Calcium Green-5N (Kd approximately 17 microM). We found that brief depolarizing pulses produced [Ca2+]i increases in a narrow somatic submembrane shell that resembled those seen in the dendrites. These results provide direct experimental evidence that the surface-to-volume ratio is a critical determinant of the spatiotemporal pattern of Ca2+ signals evoked by synaptic activity in neurons.
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002462:Cell Membrane / Q000502:physiology; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D007700:Kinetics; D051379:Mice; D018613:Microscopy, Confocal / Q000295:instrumentation / Q000379:methods; D009930:Organic Chemicals; D018408:Patch-Clamp Techniques; D011689:Purkinje Cells / Q000166:cytology / Q000502:physiology*; D051381:Rats; D015398:Signal Transduction; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure; D013997:Time Factors
D005456:Fluorescent Dyes; D009930:Organic Chemicals; C071336:calcium green; D002118:Calcium