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Biomedical subjects

D Ottoson

Publications and source records attributed to D Ottoson.

At least 19 recordsLinked to original sources
PubMed1987

Effects of a toxic phospholipase A2 (AgTx) from the venom of the Pit viper (Agkistrodon halys (Pallas)) on the crayfish stretch receptor neuron.

Neurotoxicity of an isolated fraction (V) of the venom from the snake Agkistrodon halys (Pallas) was studied on the crayfish stretch receptor using a two-electrode voltage-clamp technique. The toxin was previously shown to have less phospholipase A2 activity but to be more toxic in mice compared with bee venom phospholipase A2. At 5 micrograms ml-1 (0.35 microM) the AgTx had very little effects on the electrophysiological properties of the receptor neuron whereas at 50 micrograms ml-1 (3.5 microM) the leak conductance was increased about three times and the net outward (K) current was reduced to 70% of control. The net inward (Na) current was not affected except for a small (+ 10 mV) shift in the I-V relationship. The resting membrane potential and the membrane capacitance were not changed by AgTx. These effects of AgTx were similar to those seen after exposure to bee venom phospholipase A2 at concentrations 10-20 times lower. At concentrations of AgTx which presynaptically affect the frog neuromuscular transmission (5-10 micrograms ml-1) the effects on ion channels in the stretch receptor neuron are very small and probably reflect the low phospholipase A2 activity compared with that of bee venom phospholipase A2.

Animals↗
PubMed1985

Ionic dependence of early adaptation in the crustacean stretch receptor.

In the present study we have examined the effects of changes in potassium and calcium concentration on the early adaptation of the slowly adapting stretch receptor of the crayfish using intracellular recordings including the potential clamp technique. This was because previous studies had suggested that the early adaptative decline of the receptor potential may be attributed mainly to ionic mechanisms involved in the transducer process. During prolonged exposure to K-free saline the cell depolarized; the early adaptive fall of the receptor potential was reduced and finally the response became almost rectangular. These effects developed more rapidly if the concentration of Ca was reduced in the K-free saline. It was shown by injection of current that the effects were not potential dependent. Removal of Ca reduced the amplitude of both the dynamic and static phase of the receptor potential. Isotonic Ca-saline suppressed the static phase of the receptor potential and prolonged exposure completely abolished the response. Potential clamp experiments demonstrated that in the Ca-free saline the passive membrane conductance increased; the static phase of the receptor current increased while the peak current decreased somewhat. In the K-free and Ca-free saline both phases of the receptor current increased. The present results support earlier findings that the major part of the early adaptive fall of the receptor potential is caused by an outward K+ current. Ca2+ modifies the adaptive fall and the static phase, most likely by activation of a Ca2+-dependent K+ current and/or by inactivation of the Na+ current.

Adaptation, Physiological↗
PubMed1985

Effects of intracellular TEA injection on early adaptation of crustacean stretch receptor.

The effects of intracellular injection of TEA on the stretch-induced response of the slowly adapting stretch receptor of the crayfish have been examined to determine the contribution of an outward potassium current to the early adaptation of the neuron. Intracellular recording techniques including potential clamp measurements of membrane currents have been used. Injection of small amounts of TEA caused a pronounced depolarization of the neuron. In the early stage of depolarization there was a marked increase of the static phase of the response while the dynamic phase remained unchanged. When the resting membrane potential was kept constant by current injection both the dynamic phase and the static phase increased. However, the increase of the static phase was more pronounced than that of the dynamic phase and as a result the early phase of adaptation was almost abolished. Following TEA injection the reversal potential for both the dynamic phase and the static phase of the receptor current became somewhat more positive. TEA injection also reduced the outward current induced by a depolarizing potential step. The present results provide additional support for the hypothesis that the early phase of adaptation of the crustacean stretch receptor is attributed mainly to an outward potassium current.

Adaptation, Physiological↗
PubMed1984

Pain alleviation by vibratory stimulation.

In the present study 366 patients suffering acute or chronic musculoskeletal pain of different origin were given vibratory stimulation for the pain. Many of the patients had previously had treatments of various kinds without satisfactory relief. The effect of vibratory stimulation was assessed during and after stimulation using a graphic rating scale. Sixty-nine per cent of the patients reported a reduction of pain during vibratory stimulation. The best pain reducing site was found to be either the area of pain, the affected muscle or tendon, the antagonistic muscle or a trigger point outside the painful area. In most patients the best pain reducing effect was obtained when the vibratory stimulation was applied with moderate pressure. To obtain a maximal duration of pain relief the stimulation had to be applied for about 25-45 min.

Adolescent↗
PubMed1983

Time characteristics and potential dependence of early and late adaptation in the crustacean stretch receptor.

The receptor potential of the crustacean stretch receptor evoked by a ramp and hold stretch is depolarizing and consists of an initial peak followed by a static phase. The receptor current, defined as the stretch induced current change is inward and has a similar appearance. The adaptive fall of the receptor potential and receptor current occurs in two phases which can be separated by their different time characteristics. Using intracellular recordings including potential clamp an attempt has been made to fit experimental values of the adaptive fall of the potential and current response to a double exponential function. Ramp and hold stretches with a rise time of about 7-15 ms were used. The time constants were determined with the cell clamped or polarized to different holding potentials. It was found that the adaptive fall for both potential and current could be fitted reasonably well by double experimental functions with an initial fast phase and a second slow phase. For the potential response the time constant of the early adaptive fall, tau 1, varied with holding potential, having a minimum of approximately 3 ms at about -50 mV. tau 1 for the current response showed a similar variation with holding potential, although less pronounced than for the potential response. The minimum value was about 5 ms. The time constant, tau 2, of the late phase of adaptation both for the current and potential response was about 500 ms and did not vary in a systematic way with holding potential. The results are consistent with the idea that the first phase of adaptation is related to ionic mechanisms in the membrane of the receptor neuron while the second phase might be caused by mechanical factors.

Adaptation, Physiological↗
PubMed1982

Studies on the role of calcium in adaptation of the crustacean stretch receptor. Effects of intracellular injection of calcium, EGTA and TEA.

The effects of intracellular pressure injection of Ca2+, EGTA and TEA on the receptor potential of the crayfish stretch receptor were studied. Injection of Ca2+ caused both the transient phase and the static phase of the receptor response to diminish in amplitude, the decrease being greater for the static phase. This phase was almost abolished after a few minutes of injection. Injection of EGTA caused a decrease in the amplitude of the transient phase and an increase of the static phase. These changes progressed during the injection and finally the receptor potential became almost square. After injection of TEA the static phase increased and approached the height of the transient phase making the response almost square. The results provide evidence for the important role of intracellular Ca2+ for the adaptation of the receptor. It is suggested that the adaptive decline of the receptor potential is due to an outward potassium current which is controlled by the intracellular concentration of Ca2+.

Animals↗
PubMed1978

The effects of Triton-detergents on the stretch receptor of the crayfish.

The effects of the non-ionic detergents Triton X-45 and Triton X-100 on the action potential and the receptor potential of the stretch receptor neuron of the crayfich Astacus fluviatilis was studied with intracellular recording technique. Membrane currents were measured with voltage clamp technique. Both detergents blocked the action potential in 20--30 min at concentrations of 60--80 microgram. Following blocking of spike electrogenesis the receptor potential evoked by strech was obtained in isolation. With prolonged exposure of the neuron to the detergents there was a slowly developing reduction of the receptor potential and after 60--90 min no response to stretch could be obtained. These effects were produced without any significant change of the resting membrane potential. Following return to normal saline the responsiveness to stretch was completely restored in 80--100 min. Measurements with voltage clamp techinque showed that the passive membrane properties were little affected by the two detergents. The stretch induced current on the other hand was severely depressed and almost abolished with prolonged exposure. The experimental results suggest that non-ionic detergents block the spike electrogenesis and the transducer action by a selective action on the sodium channels of the membrane of the receptor neuron.

Action Potentials↗
PubMed1978

Crayfish stretch receptor: an investigation with voltage-clamp and ion-sensitive electrodes.

1. The membrane characteristics of the slowly adapting stretch receptor from the crayfish, Astacus fluviatilis, 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 steady-state level. 3. The stretch-induced current (SIC, where SIC = Itotal--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 O-current potential, a slow stretch-induced inward current was isolated. The latter reaches a maximum after 1 sec 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 Cl- conductance 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 stretch-induced 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) susbstituted 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 external medium. The PTris:PNa was somewhat higher (0.31) than the Parginine:PNa 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 stretch-induced current in either saline. A tenfold reduction of Ca2+ increased the conductance (at the 0-current level) about twofold. 11. Intracellular K+ and Cl- activities were obtained with ion sensitive electrodes. The average values from six cells were aiK = 133 +/- 34 mM and aiCl = 15.2 +/- 1.8 mM S.D.). EK was about 20 mV more negative than Em and ECl was about 10 mV more positive than Em. 12. aik 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.

Animals↗
PubMed1977

Responses of primary and secondary endings of isolated mammalian muscle spindles to sinusoidal length changes.

1. Responses of primary and secondary endings of isolated cat spindles to sinusoidal length changes have been recorded before and after block of impulse activity by tetrodotoxin. 2. Primary endings may discharge with each cycle of sinusoidal stretch at 25-50 Hz, with stretch amplitudes applied to the spindle poles as small as 1 micron. Thresholds are higher at lower frequencies. 3. In primary endings, amplitude of the receptor potential varies with frequency and magnitude of sinusoidal stretch. At a given stretch amplitude, the receptor-potential response increases markedly between 1 and 10 Hz. At a fixed frequency, for example, at Hz, the response to graded amplitude of sinusoidal stretch is highly nonlinear, sensitivity decreasing with large amplitudes. 4. Secondary endings show a much higher threshold than primary endings to sinusoidal stretch. Thus, at 25 Hz, secondary endings required stretch amplitudes of 50-100 micron to evoke discharge. Relatively large amplitudes of stretch were also required to evoked detectable receptor potentials. Over the range studied, the receptor potential varied more linearly with stretch amplitude in secondary than in primary endings.

Animals↗
PubMed1976

Dual role for potassium in Balanus photoreceptor: antagonist of calcium and suppression of light-induced current.

1. The mechanism of reduction and final abolition of the depolarizing receptor potential of Balanus eburneus photoreceptors in K+-free saline was examined with electro-physiological techniques including voltage-clamp and ion specific electrodes. 2. An extended exposure to K+-free saline reduces the transient peak and the steady phases of the depolarizing receptor potential by approximately equal amounts. The process can be reversed in normal saline although the wave form of the response is often more rectangular upon recovery. Restoration of K+ induces a transient hyperpolarization of the resting membrane for several minutes. 3. The depolarizing receptor potential can also be restored in K+-free solution by reducing the Ca2+ concentration. This saline depolarizes the resting membrane, and the wave form of the depolarizing receptor potential assumes a rectangular configuration. 4. Voltage-clamp experiments revealed that an extended exposure to K+-free saline produced an extreme reduction of the inward light-induced current (LIC), but no detectable change in the membrane potential at which the current reverses sign. Membrane conductance in darkness showed little change. Reduction of the Ca2+ concentration from 20 to 0-2 mM in K+-free restored the current and produced a negative 8-10 mV shift in the zero current potential. There was also a significant decrease in membrane conductance in darkness. 5. Current-voltage relations of the membrane in K+-free, low Ca2+, or K+-free low Ca2+ salines were somewhat dependent upon the order the salines were presented. 6. Low Ca2+ saline (0-2 mM) by itself produced a -5 mV shift in the zero-current potential. Removing K+ in low Ca2+ produced an additional shift (-5 mV) in the zero-current potential.

Calcium↗
PubMed1976

Initial burst of primary endings of isolated mammalian muscle spindles.

The initial burst has been studied in primary endings of isolated mammalian muscle spindles subject to controlled ramp-and-hold stretch. Near the onset of ramp stretch the primary ending discharges at a frequency dependent on stretch velocity. The initial burst is reduced or abolished by repetitive stretch. After block of impulse activity by tetrodotoxin, the receptor potential of primary endings shows an initial component, a rapid depolarization which occurs near the onset of ramp stretch at the same time as the initial burst. This initial component depends, in rate of rise and amplitude, on stretch velocity. It is also reduced or abolished by repetitive stretch. Recording of tension development by the isolated spindle in response to ramp-and-hold stretch shows an early rise in tension associated with the initial burst and the initial component of the receptor potential. This tension rise is also dependent on stretch velocity and is reduced or abolished by repetitive stretch. The results provide direct evidence that the initial burst results from mechanical factors, probably from cross bridge formation between thick and thin filaments as has been suggested (3).

Animals↗
PubMed1975

Impulse activity and receptor potential of primary and secondary endings of isolated mammalian muscle spindles.

1. An isolated muscle spindle preparation from a tail muscle of cat is described. The afferent response to a ramp-and-hold stretch was recorded in individual axons from identified primary and secondary endings. 2. Primary endings exhibit a prominent dynamic response, including an initial burst. They also show a well-maintained static discharge. Secondary endings also show a well-sustained static discharge but generally have a much lower dynamic sensitivity. The response of primary and secondary endings of the isolated spindle are similar to the typical responses seen in vivo in groups Ia or group II afferent fibres respectively. 3. Following impulse blockade by tetrodotoxin, the receptor potential was recorded from primary and from secondary endings in response to ramp-and-hold stretch. 4. During the dynamic phase the receptor potential of primary endings consists of a depolarization which has two components. (a) An initial component occurs early during ramp stretch, depends in rate of rise and amplitude on velocity of stretch and is reduced on repetitive stretch; it appears to be responsible for the initial burst. (b) A late dynamic component, which follows, is also dependent on stretch velocity and produces the late dynamic discharge. At the end of ramp stretch the receptor potential falls, and may undershoot, the static level. There is a subsequent adaptive fall during hold stretch, then a maintained static level of receptor potential. On release from stretch the membrane is hyperpolarized. 5. Secondary endings usually show a smaller dynamic response, lacking the initial component seen in primary endings. They also generally lack an undershoot following the ramp and have less of a post-release hyperpolarization. 6. Static levels of receptor potential in both primary and secondary endings are related to amplitude of stretch. 7. The receptor potentials of primary and secondary endings account for the major features of the impulse responses of these endings to ramp-and-hold stretch. In primary endings the dynamic frequencies may also depend upon a sensitivity of the impulse initiating site to rate of change of receptor current.

Animals↗