The ionic regulation of action potentials in the axon of a stretch receptor neuron of the stick insect (Carausius morosus) (original) (raw)
Related papers
Density of sodium channels in insect synaptic nerve endings
Neurochemistry International, 1990
Specific binding of [ll-3H]saxitoxin (STX) and activity of ouabain sensitive adenosinetriphosphatase (Na ÷, K+-ATPase) were determined in neuronal membrane fractions using a subcellular preparation from the central nervous system of the cockroach Periplaneta americana. The nerve ending fractions (synaptosomes) contained 90-95% of the total specific activity of ouabain sensitive Na +, K +-ATPase, and 60-70% of specific STX binding of the crude nerve homogenate. Sodium influx induced by veratridine in synaptosomes was inhibited by saxitoxin at a half-maximal concentration of 4 nM, and kinetics were consistent with reversible binding of one molecule of saxitoxin to each sodium channel receptor site, with an equilibrium dissociation constant (Ko) of approx. 3 nM. The density of saturable binding sites was 2 pmol/mg protein which was estimated to correspond to about 95 binding sites per/tm 2 of synaptic membrane. The results of transport and binding data show that insect synaptosomes possess the capability to conduct inward sodium currents at least comparable to those found in other neuronal membranes, and thus provide a physiologically viable preparation to assess the effect of cation fluxes on the synaptic transmitter release process.
Journal of Neurophysiology, 1998
Purali, Nuhan and Bo Rydqvist. Action potential and sodium current in the slowly and rapidly adapting stretch receptor neurons of the crayfish ( Astacus astacus). J. Neurophysiol. 80: 2121–2132, 1998. Action potentials (APs) and sodium current from the slowly and the rapidly adapting stretch receptor neurons in the crayfish ( Astacus astacus) were recorded with a two microelectrode voltage- and current-clamp technique. In the rapidly adapting neuron the APs had a duration of 3.2 ± 0.2 ms (means ± SE) and an amplitude of 55.2 ± 1.5 mV. In the slowly adapting receptor neuron APs had a duration of 4.1 ± 0.2 ms and an amplitude 79.9 ± 2.0 mV. APs in the rapidly adapting neuron had a larger amplitude if they were recorded from the axon. In the rapidly adapting neuron adaptation of the impulse response was prolonged by hyperpolarization or by exposure to scorpion venom. Also, sinusoidal current stimulation added to the current steps prevented impulse adaptation. Block of the potassium cur...
Solubilization and characterization of the insect neuronal sodium channel
Neuroscience Letters, 1991
Locust neuronal sodium channels were solubilized by 1% cholate and 0.2% Triton X-100, and their functionality was monitored by [~H]saxitoxin (STX) binding assays. About 40% of STX binding activity was recovered in the solubilized fraction without affecting affinity (Kd = 0.5 nM) and the time and temperature dependent STX binding activity was significantly stabilized in the presence of 20 nM STX. Partial purification by an anion exchange resin yielded a 20% recovery and a 3.5 times increase in the specific STX binding activity. Identification of the locust solubilized sodium channels by immunoprecipitation and radiophosphorylation revealed a Mr of 245,000 on SDS-PAGE. The present solubilized preparation will enable the study of the unique pharmacology of insect sodium channels.
Journal of Experimental Biology
The properties of the fast Na+ inward current of the aminergic neurosecretory dorsal unpaired median (DUM) cells isolated from the sixth abdominal ganglion of the cockroach Periplaneta americana were studied with the whole-cell clamp technique in the presence of Ca2+ and K+ channel blockers. In about 80 % of the cells, the current activated at −35 mV, was maximal at -lOmV and reversed at +48mV (Vrev), very close to VNa, the equilibrium potential for Na+ (+47.9mV). Vrev followed VNa when the external Na+ concentration was varied and the current was entirely suppressed by 1.0xlO−7moll−1 saxitoxin (STX), indicating that it was carried by Na+. In the remaining cells, an STX-sensitive maintained current was observed, the peak current-voltage relationship having almost the same Characteristics except that an additional small shoulder was present between −90 and −35 mV, suggesting the existence of two types of Na+channels. Na+ channels were half-inactivated at −41.1 mV and half-activated a...
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...
Sodium-dependent depolarizing potentials in veratrinized crayfish muscle fibres
Neuroscience Letters, 1988
In the slow abdominal flexor muscle fibers of the crayfish Procamharus clarkii, veratrinc or veratridine applied during several minutes produced the persistent transformation of the muscle fibre from a nonspiking into a Ca-dependent spiking one and spikes were followed by a long-duration depolarization. The long-duration potential depends on external Na + but is not blocked by 30 ruM tetrodotoxin (TTX). In solutions containing normal concentrations of Na + (207 mM) the absence of Ca 2 ~ or the presence of calcium channel blockers abolished both potentials. The results show that alkaloid toxins reveal a Ca-"-dependent, TTX-resistant Na + conductance in crayfish tonic muscle fibres.