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

In the present study, we used in vitro whole-cell patch-clamp technique to record and analyze oscillatory activity of neurons in the optic tectum of Xenopus. Two patterns of subthreshold oscillations were induced by long-term depolarizing current pulses. One of the oscillating patterns occurred without a slow inward current (SIC); the other was superimposed on the SIC. The subthreshold oscillations were induced by depolarization in 48% of the recorded neurons. Both the oscillations and the SIC were tetrodotoxin (TTX)-resistant, but neither occurred when the slices were immersed in Ca(2+) free solutions. The evocation of the oscillations was voltage-sensitive: only when the initial membrane potentials of the neurons were held at -40 mV or -50 mV, 10 mV depolarization could induce the subthreshold oscillations. The amplitude and duration of the SIC depended on the level of the initial membrane potential. The subthreshold oscillations might play an important role in the physiological and behavioral functions of frogs, e.g. pattern discrimination, prey recognition, avoiding behavior etc., furthermore, these oscillations might play roles in the integration of neural activity in both mammals and non-mammalian vertebrates.
Animals ; Cell Polarity ; Membrane Potentials ; Neurons ; cytology ; Patch-Clamp Techniques ; Tetrodotoxin ; pharmacology ; Xenopus

The cloned TWIK-related acid-sensitive K(+) channel (TASK-1) is sensitive to the pH changes within physiological pH range (pK~7.4). Recently, the native TASK-1-like channel was suggested to be the main contributor to the background (or leak) K(+) conductance in the motoneurons of the brain stem. Serotonin (5-HT) and variation of pH value in perfused solution could modulate these currents. Here we aimed to examine the properties and modulation of the currents by serotonin or variation of pH value in hypoglossal motoneurons of rats. Transverse slices were prepared from the brainstem of neonatal Sprague-Dawley rats (postnatal days 7-8). Hypoglossal motoneurons were used for the study. The leak K(+) current (TASK-1-like current) and hyperpolarization-activated cationic current (I(h)) were recorded with the whole-cell patch-clamp technique. The results showed that these currents were inhibited by acidified artificial cerebrospinal fluid (ACSF, pH 6.0) and activated by alkalized ACSF (pH 8.5). 5-HT (10 mumol/L) significantly inhibited both leak K(+) current and I(h) with depolarization of membrane potential and the occurrence of oscillation and/or spikes. Bath application of Ketanserine, an antagonist of 5-HT₂ receptor, reversed or reduced the inhibitory effect of acidified solution on leak K(+) current and I(h). The results suggest that 5-HT₂ receptors mediate the effects of acidified media on leak K(+) current and I(h) in hypoglossal motoneurons.
Animals ; Animals, Newborn ; Brain Stem ; cytology ; Hypoglossal Nerve ; cytology ; In Vitro Techniques ; Ion Transport ; Membrane Potentials ; Motor Neurons ; metabolism ; Patch-Clamp Techniques ; Potassium Channels, Tandem Pore Domain ; metabolism ; Rats ; Rats, Sprague-Dawley ; Serotonin ; pharmacology