Plateau potential: Supplemental material
Supplementary information for the "Plateau potential" entry in the 2003 Web-CDROM edition of the
Encyclopedia of Neuroscience, edited by George Adelman and Barry Smith (Elsevier, publ.),
maintaind by Dan Hartline. Additions, corrections and suggestions are welcome
Last update: 4/13/05
- Distribution of plateaus
- Criteria for plateaus
- Roles / properties of plateaus
- Non-neuronal plateaus
1. Updates, Feedback and Further Details
The original term "plateau potential" derived from the plateau phase in the action potential of the vertebrate heart (Wiedmann 1951). Using microelectrodes recently introduced into the electrophysiological literature by Ling and Gerard (1949), Weidmann recorded cardiac action potentials from sheep Purkinje fibers. Using a second microelectrode in the same fiber to pass current, he was able to demonstrate the all-or-nothing nature not only of the initiation of the cardiac action potential, but of its repolarization during its plateau phase. This is now recognized as a diagnostic “signature” of a plateau mechanism, derived from the “N”-shaped I(V) relation for the plateau-sustaining membrane.
3. Distribution (neural)
(For further information, click on the links)
- Spinal cord
- Thalamic relay neurons
- Perigeniculate nucleus
- Leech heart interneurons (Calabrese 1979)
- Crustacean cardiac ganglion (Tazaki and Cooke 1979)
- Crustacean stomatogastric ganglion (Russell and Hartline 1978; 1982)
- Crustacean gill-bailer system (DiCaprio 1997)
- Insect flight pattern-generator (Ramirez and Pearson 1993)
- Mollusc cerebral ganglion
- Mollusc buccal ganglion
4. Criteria for plateaus
The original defining criterion for a plateau, prolonged membrane bistability, was established by Weidmann (1951).
Several additional physiological tests for plateaus were listed by Russell and Hartline (1982) based on their studies
in lobster stomatogastric ganglion (see also Hartline and Graubard 1992 for more details). The criteria are not absolute,
and not all may be present in a plateauing cell at one time or under a given set of conditions.
Generally in the following list, the more critical criteria are listed first, followed by "softer" ones:
- Trigger test: Prolonged depolarizations (spike bursts in spiking cells) can be triggered by brief depolarizing inputs.
- Termination test: The depolarized (plateau) state can be terminated abruptly by brief hyperpolariging inputs.
- Threshold test: Triggering and termination are threshold phenomena.
- "All-or-nothing" test: Responses to both triggering and terminating stimuli are independent of the magnitude of the
- Regenerative test: Responses grow after the end of a stimulus in either depolarizing or hyperpolarizing direction.
- Refractoriness test: following all-or-nothing termination of a depolarized state, it is more difficult to trigger
a second plateau (typical but not essential).
- Symmetrical pulse test: Comparing responses to depolarizing and hyperpolarizing pulses, the membrane response is
greater in the direction of the transition (depolarizing from a rest state; hyperpolarizing from a plateau state).
- Accelerating trajectory test:Characteristic accelerating membrane potential trajectories, in both depolarizing and
hyperpolarizing directions in response to injected current.
- Membrane potential excursion test: Larger membrane potential excursions occur than can be accounted for on the basis of
observed synaptic inputs.
- Critical hyperpolarization test: Membrane potential oscillation amplitude is suppressed in an all-or-nothing manner
at some point as hyperpolarizing current offset is increased. The "all-or-nothing" character may occur as "missed" bursts
in an ongoing pattern (EPSPs typically grow in magnitude with hyperpolarization owing to reversal potential effects).
- "Discontinuous" V(I) test: Isochronal V(I)) curves (voltage response at a fixed time folllowing onset of an injected
current) show abrupt transitions from more hyperpolarized to more depolarized states or the reverse
as injected current is slowly changed.
- Graded burst-rate test: Overall burst rates or periods of depolarization in an ongoing network pattern are modulated
by sustained injection of current. Bursts of spikes are less frequent as the cell is artificially hyperpolarized.
If the cell is being driven by a network, this is manifest by the "skipping" of burst activity cycles rather than the smooth
gradation in burst rates seen in pacemaker bursters.
- Endogenous burst test: If rhythmic synaptric driving is eliminated, endogenous repetitive bursting may result if
restorative and "pacemaker" mechanisms are present; note that other mechanisms for endogenous
repetitive bursting are also found in neurons.
5. Ionic mechanisms
Plateaus described to date derive from voltage-dependent inward current mechanisms that produce an "N"-shaped I(V) relation in the membrane.
The negative slope region of this relation (regenerative characteristic) results in two points of stable membrane potential, one near rest
and the other in a depolarized "plateau" state. Two mechanisms, calcium and persistent sodium, are the primary ones involved.
- Calcium currents: In mammalian cells, the low threshold "T" current has had recent interest.
- Persistent sodium current: Recently, the widespread occurrence of a TTX-sensitive I(NaP) has been recognized (not always
in conjunction with plateaus, but relevant thereto). See for example Clay (2003); Powers & Binder (2003). There is evidence for
Na involvement in certain (but not all) plateaus in stomatogastric gangklion.
6. Roles/Properties of plateaus
Plateaus promote a variety of characteristics in cells possessing them.
- Burst formation
- Quasistable switch-like properties: either "on" or "off"
- Temporal contrast: abriupt transitions between silence and high-frequency firing
- Increased "gain" for synaptic input: weak inputs can control (initiate or terminate) strong output
- Source of strong depolarization, hence high-frequency firing.
- "Trigger" mode operation: Output consequences outlast the brief inputs that trigger them
- Opportunities for regulatory control via modulatory input
- Wind up in firing freuqency
7. Non-neuronal plateaus
Plateaus are found in a variety of non-neural cell types:
- Vertebrate heart:
The original locus where plateau potentials were discovered (Weidmann, 1951).
- Vertebrate smooth muscle:
- Pancreatic cells:
- Protozoans: Presence of a mechanism promoting bistability in membrane potential has been reported in ciliates (Rudberg and Sand 2000)
9. Citations for this page
Clay JR On the persistent sodium current in squid giant axons (2003) J Neurophysiol89: 640-644
Hartline, D. K. and Graubard, K. (1992) "Cellular and synaptic properties in the crustacean stomatogastric nervous system" in Harris-Warrick, R.M., Marder, E., Selverston, A.I. and Moulins, M. (eds) Dynamic Biological Networks: The Stomatogastric Nervous System MIT PRess: Cambridge, MA pp 31-85.
Ling G., and Gerard, R.W. (1949) J. cell. Comp. Physiol. 34: 383 –
Powers RK, and Binder MD (2003) Persistent sodium and calcium currents in rat hypoglossal motoneurons J Neurophysiol 89: 615-624 abstract
Ramirez, J-M and Pearson, K.G. (1993) "Alteration of bursting properties in interneurons during locust flight" J. Neurophysiol. 70: 2148-
Rudberg P. and Sand, O. (2000) "Bistable membrane potential of the ciliate Coleps hirtus". J exp Biol. 203: 757-64.
Russell, D.F. and Hartline, D.K. (1982) "Slow active potentials and bursting motor patterns in pyloric network of the lobster Panulirus interruptus J. Neurophysiol. 48: 914-937 [PDF]
Weidmann, S. (1951): Effect of current flow on the membrane potential of cardiac muscle. J Physiol Lond 115: 227-236
10. Recent literature
Hornby TG, Rymer WZ, Benz EN, and Schmit BD (2003) Windup of flexion reflexes in chronic human spinal cord Injury:
A marker for neuronal plateau potentials? J Neurophysiol 89: 416-426
Links to related sites
Hartline Home Page.
Stomatogastric Nervous System web site
Pacemaker potential page.