Biomedical subjects
Publications and source records attributed to H Washio.
Potassium contracture consists of a phasic and a sustained component. Extracellular Ca ions are essential for both components. In the phasic component the Ca-induced Ca release mechanism is activated by the entry of the Ca ions.
The activities of choline acetyltransferase (CAT) and acetylcholinesterase (AChE) were assayed in intact diaphragm, extensor digitorum longus (EDL), and soleus muscles or their homogenates of young (2-6 months) and aged (24-34 months) mice. CAT activity (per mg of protein) was significantly higher in diaphragm and soleus of old mice in comparison with the young but the age change in EDL was negligible. On the other hand, AChE activity (per mg of protein) was significantly higher in EDL of old mice but in diaphragm and soleus muscles the enzyme activity did not show any significant change statistically. The diaphragm muscle was divided into two fractions, one being neuromuscular (NM) fraction and the other the remainder of the muscle (M fraction). No appreciable change in the ratio of the enzyme activities of NM fraction to the one of M fraction was obtained between the young and aged preparations. Thus, it seems likely that there is an age-related change in CAT and AChE activities which might be affected by the degree to which muscle activity is maintained.
1. The effects of denervation on the mechanical responses to various concentrations of L-glutamate in retractor unguis muscle of cockroach (Perilpaneta americana) was examined, comparing them with contractures induced by high potassium saline. 2. The dose-response curve was shifted to the lower concentrations of L-glutamate after 9 days of denervation. 3. Following a transient increase in the maximum contracture tension, it decreased with days after denervation and reached a constant level by several days. However, from 16 to 20 days after denervation, the tension ratios of the maximum glutamate to potassium contractures were significantly higher than that of the innervated muscles. 4. A sustained contracture was observed on and after treatment of L-glutamate in the denervated muscle. Pretreatment of the muscle by concanavalin A facilitated to induce L-glutamate contracture. 5. It was suggested that the sensitivity of the muscle membrane to L-glutamate was increased in the denervated muscle.
The cholinesterase activity at the motor end-plate of aged mice was investigated histochemically. A relative quantitative method was applied for studying the reaction at end-plates by utilizing varying concentrations of eserine. The number of end-plates reacting at a concentration of more than 5 X 10(-6) M eserine was reduced in aged diaphragm but increased in aged soleus muscle at 10(-5) M eserine in comparison with those in the young. It seems likely that there is an age-related change in cholinesterase activities in relation to muscle fiber types.
The effect of extracellular nickel on the excitatory postsynaptic response at the insect neuromuscular junction was studied in the segmental muscle of the larval mealworm Tenebrio molitor. The response to L-glutamate applied iontophoretically (glutamate potential, GP) was potentiated in the presence of Ni2+ though the excitatory postsynaptic potential (EPSP) was reduced. It seems unlikely that Ni2+ acts at the same binding site as L-glutamate does since the value of the limiting slope of double logarithmic plots for the action of glutamate was increased in the presence of Ni2+. The potentiation of GP in the presence of Ni2+ cannot be ascribed to competition between Ni2+ and Ca2+ since GP amplitude did not show any dependence on the concentration of Ca2+. Nickel ions did not alter the reversal potential of excitatory postsynaptic current (EPSC) and glutamate current (GC) under the voltage clamp condition, whereas the amplitude of GC was potentiated in the presence of Ni2+. The time constant of the decay of EPSC showed a weak voltage dependency: the more depolarized the membrane, the more prolonged the time constant. In the presence of 1 mM Ni2+ the amplitude of miniature EPSCs (MEPSCs) increased and the half decay time was prolonged significantly. These results suggest that Ni2+ interacts with charged groups near the glutamate receptor-channel complex so that the kinetics of the channel are altered.
The effect of streptomycin on the neuromuscular junction of the cockroach leg muscle was studied by means of intracellular electrodes. The miniature excitatory postsynaptic potential (MEPSP) frequency decreased in the presence of 1 mM streptomycin. Double logarithmic plots of the quantal content against the external calcium concentration in the absence and presence of streptomycin suggested the competition for a common site of presynaptic membrane at insect neuromuscular junctions.
On the dorsal surface in the metathoracic ganglion of the cockroach Periplaneta americana, eight large and a number of small somata described by Crossman et al., (1971) were reexamined. These eight large cells (40-60 micron in diameter) could be divided into three different types by Lucifer yellow or nickel injection, depending on the branching of their axons. No neuron was found which sent axons into either the anterior or posterior connectives. In the mesothoracic ganglion an interganglionic H-shaped DUM neuron was found which had four axons, one into each anterior and posterior connective.
The effect of maitotoxin (MTX), the most potent marine toxin as yet known, was studied using the skeletal muscle of the larval meal worm, Tenebrio molitor. In normal saline, Tenebrio muscles responded with the spike to direct stimulation. In the saline containing tetraethylammonium (TEA) the all-or-none action potential which had characteristic plateau was elicited by membrane depolarization. When MTX (5 X 10(-9) to 10(-8) g/ml) in the TEA saline was added, the plateau of action potential was prolonged more than in the saline containing TEA alone. Furthermore, MTX lowered the threshold, so that action potentials were readily evoked in the saline containing MTX. In either case, effects, of MTX were antagonized by Co2+. These results suggest that MTX activates the voltage-dependent Ca2+ channels in the insect muscle.
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The effect of extracellular lanthanum on neuromuscular transmission was studied in cockroach leg muscle and larval mealworm ventral muscle by means of microelectrodes. Miniature excitatory postsynaptic potential (MEPSP) frequency was markedly increased after lanthanum was added, in the presence and absence of calcium. The potentiation by La3+ was suppressed in a high Ca2+ saline and enhanced in the absence of Ca2+. Lanthanum ions blocked neuromuscular transmission at a concentration as low as 0.1 mM. The quantal content estimated by the failure method was reduced by 80% in the presence of 0.1 mM-La3+. The reduction in the EPSP amplitude by La3+ may be due to a decrease in the amount of transmitter released by a nerve impulse. The response to L-glutamate applied iontophoretically was also reduced in the presence of La3+. It seems unlikely that La3+ and L-glutamate were competing for a common binding site on the postsynaptic membrane since the apparent maximum of the dose-response curve for glutamate-induced depolarization was reduced in the presence of La3+. External recording of MEPSPs showed that adding lanthanum to the bathing medium increased the time constant of decay of the potential. These results suggest that lanthanum does indeed have a postsynaptic action in addition to its prejunctional action in insect muscle fibres.
1. The effect of uncoupling agents of oxidative phosphorylation, potassium warfarin and carbonylcyanide-p-trifluoromethoxy-phenylhydrazone (p-CCP), on the spontaneous release of transmitter was studied at the neuromuscular junction of cockroach muscles. 2. The agents produced a large increase in the frequency of occurrence of miniature excitatory postsynaptic potentials (MEPSPs). This increase also was observed in calcium-free saline. 3. The results may be explained on the hypothesis that the increase in the spontaneous release is due to the increase in free calcium concentration derived from an intracellular origin in the terminal. The mitochondria may play an important role in regulating the intracellular calcium concentration in the nerve terminals of insect muscles.
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1. The effect of extracellular cobalt on the frequency of miniature excitatory post-synaptic potentials (MEPSPs) was studied in cockroach leg muscle fibres that had been depolarized with 20.8 mM-K saline. 2. Cobalt ions had a dual effect on the spontaneous release of transmitter, an inhibitory action being followed by an acceleratory. A reciprocal relationship between Ca2+ and Co2+ was found for both the inhibitory and acceleratory effects. 3. The equilibrium dissociation constant for Co2+ as a competitive antagonist of spontaneous release ranged from 0.4 to 0.65 mM. It is concluded that Co2+ is much more potent than Mg2+ in suppressing spontaneous transmitter release at the insect neuromuscular junction. The antagonism by extracellular Co2+ appears to occur only at the external surface site on the terminal membrane.
The skeletal muscle of members of Orthoptera and Diptera receives an innervation which is probably glutaminergic. Recent study of the ventral muscle fibres in the larvae of the beetle, Tenebrio molitor, has revealed that the transmitter action can be mimicked by the iontophoretic application of L-glutamate to the junctional sites at which the extracellular excitatory postsynaptic potentials (e.p.s.ps) could be recorded (D.Y. and H.W., unpublished observation). Contrary to the evidence favouring glutamate as a transmitter of junctional excitation in insects, some investigators have found that curare (+)tubocrarine, TC), a classic acetylcholine (ACh) antagonist, suppresses the neurally evoked muscle potentials in the fly Sacophaga, and Tenebrio. Here, we have analysed the action of curare on the neuromuscular junction of Tenebrio larvae and found that curare blocked the glutaminergic transmission by antagonising the transmitter at the postsynaptic site.
The contribution of Na ions to the electrically excited response was studied in the muscle fibres of mealworm larvae, Tenebrio molitor, using microelectrode techniques. When Ca ions were omitted from the external solution, no action potential could be elicited. However, addition of Na ions to Ca-free medium rendered the fibre excitable again. The amplitude of these action potentials increased with a slope of about 40 mV for a 10-fold elevation of external Na concentrations. Tetrodotoxin had no effect on the initiation of the spike, and Co ions completely suppressed it. Therefore, it seems likely that a Ca-channel, which is utilized by both Na and Ca ions, is the sole factor responsible for the action potential in the mealworm larval muscle fibre membrane.
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