Experiments were performed to study the voltage-dependence of miniature inhibitory postsynaptic current (mIPSC) frequency and amplitude using patch-clamp technique with whole cell recording in optic tectal slices of Xenopus. The following results have been observed. (1) When the membrane potentials of a neuron were depolarized or hyperpolarized stepwise from a resting potential via recording pipette to inject a DC current, the frequency and/or amplitude of mIPSCs increased or decreased respectively. The frequency of mIPSCs increased gradually with depolarizing membrane potential and it attained to the maximum as the membrane potential was held at +10 mV. (2) The amplitude increased slightly as the neuron was depolarized. When the depolarization of membrane potential reached -30 or -40 mV, the amplitudes of mIPSCs were maximal. Further depolarization resulted in a decrease of amplitude. Meanwhile, the large mIPSCs appeared when the membrane potential depolarized to a range between -20 mV and +10 mV. (3) With Ca(2+)-free bath solution, the frequency and amplitude of mIPSCs also increased stepwise progressively on depolarization of membrane potential, but the increase was less marked as corresponding value in normal saline perfusion. (4) When the [K(+)](o) in bath solution increased, the frequency of mIPSCs decreased markedly and the amplitude of mIPSCs decreased slightly. If the external K(+) concentration increased further to higher than 20 mmol/L, the neuron produced a marked slow inward or outward membrane current. The possible mechanism underlying the voltage-dependence of mIPSC frequency and amplitude is discussed briefly.
Animals ; Brain ; cytology ; physiology ; Inhibitory Postsynaptic Potentials ; physiology ; Membrane Potentials ; physiology ; Miniature Postsynaptic Potentials ; physiology ; Neurons ; physiology ; Patch-Clamp Techniques ; Potassium Channels, Voltage-Gated ; physiology ; Xenopus

Amyotrophic lateral sclerosis (ALS) is a degenerative neuromuscular disease of unknown etiology in which the upper and lower motor neurons are progressively destroyed. Recent evidences support the role of autoimmune mechanisms in the pathogenesis of ALS. This study investigated the effects of sera from ALS patients on neuromuscular transmission in phrenic nerve-hemidiaphragm preparations and on calcium currents of single isolated dorsal root ganglion (DRG) cells in mice. Mice were injected with either control sera from healthy adults or ALS sera from 18 patients with ALS of sporadic form, for three days. Miniature end plate potential (MEPP) and nerve-evoked end plate potential (EPP) were measured using intracellular recording technique and the quantal content was determined. Single isolated DRG cells were voltage-clamped with the whole-cell configuration and membrane currents were recorded. Sera from 14 of 18 ALS patients caused a significant increase in MEPP frequency in normal Ringer's solution (4.62+/-0.14 Hz) compared with the control (2.18+/-0.15 Hz). In a high Mg2+/low Ca2+ solution, sera from 13 of 18 ALS patients caused a significant increase in MEPP frequency, from 2.18+/-0.31 Hz to 6.09+/-0.38 Hz. Sera from 11 of 18 patients produced a significant increase of nerve-evoked EPP amplitude, from 0.92+/-0.05 mV to 1.30+/-0.04 mV, while the other seven ALS sera did not alter EPP amplitude. In the ALS group, EPP quantal content was also elevated by the sera of 14 patients (from 1.49+/-0.07 to 2.35+/-0.07). MEPP frequency and amplitude in wobbler mouse were 4.03+/-0.53 Hz and 1.37+/-0.18 mV, respectively, which were significantly higher than those of wobbler controls (wobblers without the symptoms of wobbler). Sera from ALS patients significantly reduced HVA calcium currents of DRG cells to 42.7% at -10 mV. Furthermore, the inactivation curve shifted to more negative potentials with its half-inactivation potential changed by 6.98 mV. There were, however, significant changes neither in the reversal potential of ICa nor in the I-V curve. From these results it was concluded that: 1) The serum factors of sporadic ALS patients increase neuromuscular transmission and can alter motor nerve terminal presynaptic function. This suggests that ALS serum factors may play an important role in the early stage of ALS, and 2) Calcium currents in DRG cells were reduced and rapidly inactivated by ALS sera, suggesting that in these cells, ALS serum factors may exert interaction with the calcium channel.
Adult ; Amyotrophic Lateral Sclerosis* ; Animals ; Calcium Channels* ; Calcium* ; Diagnosis-Related Groups ; Excitatory Postsynaptic Potentials ; Ganglia, Spinal ; Humans ; Membranes ; Mice* ; Miniature Postsynaptic Potentials ; Motor Neurons ; Neuromuscular Diseases ; Neuromuscular Junction