scholarly journals Extending the realm of membrane capacitance measurements to nerve terminals with complex morphologies

2010 ◽  
Vol 588 (12) ◽  
pp. 2011-2012 ◽  
Author(s):  
Mean‐Hwan Kim ◽  
Henrique Von Gersdorff
Keyword(s):  
Membrane Capacitance ◽  
Nerve Terminals ◽  
Capacitance Measurements

How Neurons Communicate: Gap Junctions and Neurosecretion

The Neuron ◽  
2015 ◽  
pp. 153-186
Author(s):  
Irwin B. Levitan ◽  
Leonard K. Kaczmarek
Keyword(s):  
Synaptic Vesicles ◽  
Fluorescent Dyes ◽  
Imaging Techniques ◽  
Electrical Coupling ◽  
Snare Complex ◽  
Biologically Active ◽  
Nerve Terminals ◽  
Capacitance Measurements ◽  
Complex Process ◽  
Cytoplasmic Vesicles

Two ways that neurons communicate with one another are by direct electrical coupling and by the secretion of neurotransmitters. Electrical coupling arises from the existence of proteins, known as connexins, that form pores linking the cytoplasm of adjacent cells. Ions and small molecules can carry signals from one cell to another through these pores. Neurosecretion is a more complex process whereby different categories of molecules are sorted into cytoplasmic vesicles. Chemical processes within these vesicles ensure that they contain biologically active transmitters or hormones. SNARE complex proteins cooperate with other proteins to allow synaptic vesicles containing neurotransmitter to release their components into the external medium following calcium entry into nerve terminals. Such exocytosis of synaptic vesicles can be monitored with imaging techniques using fluorescent dyes or proteins, or by capacitance measurements. A second set of molecules retrieves the membrane of synaptic vesicles back from the plasma membrane through endocytosis.

Capacitance Measurements in the Mouse Rod Bipolar Cell Identify a Pool of Releasable Synaptic Vesicles

2006 ◽  
Vol 96 (5) ◽  
pp. 2539-2548 ◽  
Author(s):  
Zhen-Yu Zhou ◽  
Qun-Fang Wan ◽  
Pratima Thakur ◽  
Ruth Heidelberger
Keyword(s):  
Bipolar Cell ◽  
Synaptic Vesicles ◽  
Sine Wave ◽  
Membrane Capacitance ◽  
Membrane Properties ◽  
Intact Mouse ◽  
Time Resolved ◽  
Capacitance Measurements ◽  
Treatment Conditions ◽  
Capacitance Response

The mouse is an important model system for understanding the molecular basis of neuronal signaling and diseases of synaptic communication. However, the best-characterized retinal ribbon-style synapses are those of nonmammalian vertebrates. To remedy this situation, we asked whether it would be feasible to track synaptic vesicle dynamics in the isolated mouse rod bipolar cell using time-resolved capacitance measurements. The results demonstrate that membrane depolarization triggered an increase in membrane capacitance that was Ca2+ dependent and restricted to the synaptic compartment, consistent with exocytosis. The amplitude of the capacitance response recorded from the easily accessible soma of an intact mouse rod bipolar cell was identical to that recorded directly from the small synaptic terminal, suggesting that in the carefully selected cohort of cells presented here, axonal resistance was not a significant barrier to current flow. This supposition was supported by the analysis of passive membrane properties and a comparison of membrane capacitance measurements in cells with and without synaptic terminals and reinforced by the lack of an effect of sine-wave frequency (200–1,600 Hz) on the measured capacitance increase. The magnitude of the capacitance response increased with Ca2+ entry until a plateau was reached at a spatially averaged intraterminal calcium of about 600 nM. We interpret this plateau, nominally 30 fF, as corresponding to a releasable pool of synaptic vesicles. The robustness of this measure suggests that capacitance measurements may be used in the mouse rod bipolar cell to compare pool size across treatment conditions.

scholarly journals Membrane Capacitance Measurements Revisited: Dependence of Capacitance Value on Measurement Method in Nonisopotential Neurons

2009 ◽  
Vol 102 (4) ◽  
pp. 2161-2175 ◽  
Author(s):  
Jorge Golowasch ◽  
Gladis Thomas ◽  
Adam L. Taylor ◽  
Arif Patel ◽  
Arlene Pineda ◽  
...  
Keyword(s):  
Surface Area ◽  
Voltage Clamp ◽  
Computational Models ◽  
Model Neuron ◽  
Compartment Model ◽  
Membrane Capacitance ◽  
Current Clamp ◽  
Capacitance Measurements ◽  
Fitting Procedures ◽  
Total Membrane

During growth or degeneration neuronal surface area can change dramatically. Measurements of membrane protein concentration, as in ion channel or ionic conductance density, are often normalized by membrane capacitance, which is proportional to the surface area, to express changes independently from cell surface variations. Several electrophysiological protocols are used to measure cell capacitance, all based on the assumption of membrane isopotentiality. Yet, most neurons violate this assumption because of their complex anatomical structure, raising the question of which protocol yields measurements that are closest to the actual total membrane capacitance. We measured the capacitance of identified neurons from crab stomatogastric ganglia using three different protocols: the current-clamp step, the voltage-clamp step, and the voltage-clamp ramp protocols. We observed that the current-clamp protocol produced significantly higher capacitance values than those of either voltage-clamp protocol. Computational models of various anatomical complexities suggest that the current-clamp protocol can yield accurate capacitance estimates. In contrast, the voltage-clamp protocol estimates rapidly deteriorate as isopotentiality is reduced. We provide a mathematical description of these results by analyzing a simple two-compartment model neuron to facilitate an intuitive understanding of these methods. Together, the experiments, modeling, and mathematical analysis indicate that accurate total membrane capacitance measurements cannot be obtained with voltage-clamp protocols in nonisopotential neurons. Furthermore, although current-clamp steps can theoretically yield accurate measurements, experimentalists should be aware of limitations imposed by step duration and numerical errors during fitting procedures to obtain the membrane time constant.

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