The ionic regulation of action potentials in the axon of a stretch receptor neuron of the stick insect (Carausius morosus) (original) (raw)
Ionic bases of action potentials in identified flatworm neurones
Journal of Comparative Physiology A, 1984
The ionic bases for generation of action potentials in three types of identified multimodal neurones of the brain of Notoplana acticola, a polyclad flatworm, were studied. The action potentials were generated spontaneously, in response to water-borne vibrations, or by intracellularly injected current pulses. At least three components comprise the depolarizing excitable phase of the action potentials: (a)a rapidly inactivating TTXsensitive Na + component ; (b) a Ca ++ component that is unmasked by intracellular TEA + ; (c)a TTX-resistant Na + component . Two K + currents appear to account for the repolarization phase of the action potentials: (a) a rapid K + current that is blocked by intracellular TEA + and (b) a Ca + +-activated K + conductance that is blocked by Ca + + and Ba § + . Ionic mechanisms in the generation of action potentials in the central multimodal neurones of Notoplana pharmacologically resemble those in higher metazoans.
The Journal of experimental biology, 2000
The efferent dorsal unpaired median (DUM) neurones, which include octopaminergic neurones, are among the most intensively studied neurones in the insect central nervous system. They differ from other insect neurones in generating endogenous spontaneous overshooting action potentials. The second half of the 1980s is certain to be considered a turning point in the study of the ion channels underlying the electrical activity of DUM neurones. Recent advances made using the patch-clamp technique have stimulated an increasing interest in the understanding of the biophysical properties of both voltage-dependent and voltage-independent ion channels. Patch-clamp studies of DUM neurones in cell culture demonstrate that these neurones express a wide variety of ion channels. At least five different types of K(+) channel have been identified: inward rectifier, delayed rectifier and A-like channels as well as Ca(2+)- and Na(+)-activated K(+) channels. Moreover, besides voltage-dependent Na(+) and...
Crayfish stretch receptor: an investigation with voltage-clamp and ion-sensitive electrodes
The Journal of Physiology, 1978
1. The membrane characteristics of the slowly adapting stretch receptor from the crayfish, Asta8us fiuviatilis, were examined with electrophysiological techniques consisting of membrane potential recording, voltage clamp and ion-sensitive microelectrodes. 2. The passive membrane current (Ip) following step changes of the membrane potential to levels above 0 mV required more than a minute to decay to a steadystate level. 3. The stretch-induced current (SIC, where SIC = total-Ipassive) was not fully developed until the Ip had decayed to a steady state. 4. With Ip at the steady state and the stretch-induced current at the 0-current potential, a slow stretch-induced inward current was isolated. The latter reaches a maximum after 1 see of stretch and declines even more slowly after stretch. The I-V relation of the slow current had a negative slope and reversed sign near the resting potential. It is suggested that this current is due to a Clconductance change. 5. The stretch-induced current, consisting of a rapid transient phase and a steady component can be isolated from the slow stretch-induced current at a holding potential corresponding to the resting potential. 6. The SIC-Em relation is non-linear and reverses sign at about +15 mV. 7. In a given cell, the reversal potential of the stretch-induced potential change obtained with current clamp coincided with the 0-current potential of the stretchinduced current obtained by voltage clamp. The average value from twenty-six cells was + 13 + 6'5 mV; cell to cell variability seemed to be correlated with dendrite length. 8. Tris (mol. wt. 121) or arginine (mol. wt. 174) substituted for Na+ reduces but does not abolish the stretch-induced current. 9. The permeability ratios of Tris: Na and arginine: Na were estimated from changes in the 0-current potential as these cations replaced Na+ in the eternal medium. The PTr, :PNa was somewhat higher (0-31) than the Parginine:PN ratio (0.25). 10. Changes in the external Ca2+ concentration had no effect on the 0-current potential in Na or Tris saline. However, reducing Ca2+ did augment the stretchinduced current in either saline. A tenfold reduction of Ca2+ increased the conductance (at the 0-current level) about twofold. H. M. BROWN AND OTHERS 11. Intracellular K+ and Clactivities were obtained with ion sensitive electrodes. The average values from six cells were ai = 133 + 34 mM and ai i = 15-2 + 1-8 mM S.D.). EK was about 20 mV more negative than Em and EC1 was about 10 mV more positive than Em. 12. act and resting Em undergo large changes in K+-free solutions. After 60 min, ak was reduced eightfold and Em was reduced from-67 to-40 mV. Reduced Ca2+ in K+-free augments the rate of these changes. Receptor potential amplitude was also reduced in K+-free solution but could be restored upon polarizing the membrane to the pre-existing resting level.
Journal of Experimental Biology
Adult neurones were obtained by dissociation of the dorsal area of the sixth abdominal (A6) ganglion of the cockroach, and electrical properties were studied with the patch-clamp technique. The neurones showed spontaneous fast action potentials, similar to those recorded with microelectrodes in neurones in situ along the dorsal median line of the A6 ganglion. Synthetic saxitoxin (sSTX) at concentrations of 10 × 10−8 to 1.0×10−7mol l−1 suppressed the action potential (AP) and induced a dose-dependent hyperpolarization of the resting potential, suggesting that two types of sSTX-sensitive Na+ channels are present. The resting potential was dependent on the external concentration of both Na+ and K+, with a similar sensitivity to each, yielding a slope of about 43 mV per 10-fold change in concentration. The delayed outward rectification present under control conditions was reduced by tetraethylammonium chloride (TEA-Cl, 1.0×10−2mol l−1). TEA-Cl or Ca2+-free saline abolished the afterhype...
Identification of ionic currents at presynaptic nerve endings of the lizard
The Journal of physiology, 1989
1. Ionic currents associated with the invasion of an action potential into the motor nerve ending of the lizard, Anolis carolinensis, were measured with a focal extracellular electrode at several locations along the nerve ending. 2. These experimentally observed currents could be matched with computer simulations of action potential propagation into the nerve ending. They revealed that while Na+ channels are the major ionic current pathway in the heminode, K+ channels provide the major pathway in the terminal branches and boutons. 3. Calcium current in the presynaptic ending was unmasked by the application of tetraethylammonium (TEA). This current was blocked by: (a) cadmium, (b) omega-conotoxin GVIA and (c) nifedipine, but was unaffected by nickel at concentrations less than or equal to 100 microM. Nifedipine's action became more definitive when the duration of the action potential was greatly extended by pre-treatment with TEA. The effect of Bay K 8644 was inconsistent. 4. Tra...
Brain Research, 1999
Ž. Inward Na currents were studied, using a two-microelectrode intracellular voltage-clamp technique, in the slowly adapting SA and Ž. rapidly adapting RA stretch receptor neurons of the crayfish after the axons were cut at different distances from the soma. In the SA neuron, inward Na q currents were recorded in the soma even when the axon was cut as close as 100 mm from the center of the soma, indicating the presence of Na q channels in these parts. Also, two populations of Na q channels seem to exist in the SA neuron. In the RA neuron, only minute Na q currents were observed if the axon was shorter than 250 mm. The results strongly indicate that the voltage-gated Na q channels in the SA and RA neurons have different distributions and that the difference in the spatial distribution of Na q channel types may be important for the difference in firing properties in the two types of neurons.
Ionic mechanisms of 3 types of functionally different neurons in the lamprey spinal cord
Brain Research, 1985
Action potentials and afterpotentials were compared in giant interneurons, sensory dorsal cells and large intraspinal axons in the lamprey spinal cord. Afterpotentials of giant interneurons and dorsal cells consisted of two hyperpolarizing phases, an early and a late one, which were separated by a delayed depolarization. The afterpotentials of axons had a single hyperpolarizing phase also followed by a delayed depolarization. Tetraethyl ammonium chloride (TEA+) eliminated the early phase of the afterhyperpolarization in giant interneurons, only partially reduced the early phase in dorsal cells and did not affect the single phase of axons. The delayed depolarization of dorsal cells was attenuated by TEA+ but in axons it was unaltered. The heavy metal ions Mn2+ and Co2+ (2 mM) eliminated the late phase in giant interneurons but did not reduce the late phase in dorsal cells. The delayed depolarization remained in both types of cell in the presence of these ions. Action potentials of giant interneurons and dorsal cells, but not those of axons, were broadened by TEA+. The TEA-prolonged action potentials were narrowed by Mn2+ applied in combination with TEA+. The afterhyperpolarizations of all 3 cells were reduced by injection of negative current and enhanced by positive current. Repetitive stimulation resulted in summation of the afterhyperpolarization in giant interneurons and dorsal cells. The results suggest that different sets of potassium channels are responsible for the afterhyperpolarizations in each type of cell. In giant interneurons fast channels which are sensitive to TEA+ may underlie the early phase and slow channels activated by calcium entry may underlie the slow phase. The early phase of dorsal cells may be caused by two types of fast channel, one similar to that in giant interneurons and another less sensitive to external TEA+. This latter type may also cause the afterhyperpolarization in axons. Although calcium channels appear to contribute to the action potentials of giant interneurons and dorsal cells, the late phase of the latter neurons does not seem to be activated by calcium entry. The delayed depolarizations of the neurons appear to be due to an inward current which is not carried by calcium.
Pflügers Archiv - European Journal of Physiology, 2011
The effects of antidromic potential spread were investigated in the stretch receptor neurons of the crayfish. Current and potential responses to conductance changes were recorded in the dynamic clamp condition and compared to those obtained by using some conventional clamp methods and a compartmental neuron model. An analogue circuit was used for dynamic calculation of the injected receptor current as a function of the membrane potential and the given conductance change. Alternatively, receptor current responses to a mechanical stimulus were recorded and compared when the cell was voltage clamped to a previously recorded impulse wave form and the resting potential, respectively. Under dynamic clamp, the receptor current had an oscillating waveform which contrasts with the conventional recordings. Frequency, amplitude and sign of the oscillations were dependent on the applied conductance level, reversal potential and electrotonic attenuation. Mean current amplitude and frequency of the evoked impulse responses were smaller under dynamic clamp, especially for large conductance increases. However, firing frequency was larger if plotted against the mean current response. Recorded responses were similar to those calculated in the model. It was not possible to evoke any adaptation in the slowly adapting neuron by using the dynamic clamp. Evoked potential change served as a self limiting response, preventing the depolarization block. However, impulse duration was significantly shorter in the rapidly adapting neuron when the dynamic clamp was used. It was concluded that, in the stretch receptor neurons during a conductance increase, antidromic potential spread modulates the receptor responses and contributes to adaptation.
Sodium channel distribution in a spider mechanosensory organ
Brain Research, 1995
A site-directed antibody was used immunocytochemically to measure the distribution of sodium channels in the tissues of a spider mechanoreceptor organ. The VS-3 slit sense organ contains 7-8 pairs of bipolar sensory neurons; these neurons are representative of a wide range of arthropod mechanoreceptors. Sensory transduction is thought to occur at the tips of the dendrites and to cause action potentials that are regeneratively conducted to the cell bodies, although it has not been possible to confirm this by direct intracellular recordings from the dendrites. Wholemount preparations were labelled by immunofluorescence and thin sections were immunogold labelled, using an antibody to the highly conserved SP19 sequence of the voltage-activated sodium channel. Labelling for sodium channels was found in the neurons and in their surrounding glial cells. Both cytoplasm and membranes were labelled, but immunogold particles were clearly aligned along cell membranes, indicating that the majority of labelling represented membrane-bound sodium channels. Channel density in the dendrites was similar to the axons and higher than in the cell bodies, supporting the idea of active conduction in the sensory dendrites. Labelling in glial cell membranes was indistinguishable from the neighboring neurons, suggesting a significant role for sodium channels in the functions of these supporting cells.