Nervous System of Periplaneta americana Cockroach as a Model in Toxinological Studies: A Short Historical and Actual View

Figure 2

Single-fiber double-oil-gap method on isolated giant axon. (a) Electronic arrangement of technique for current- and voltage-clamp recordings (CC and VC, resp.)—according to [4]. α and β are the lateral (recording and stimulating) electrodes immersed in 180 mM KCl—they have contact with the cut ends of axons in connective and represent intracellular electrodes; γ electrode is plunged in physiological saline (with the tested substances)—it has contact with the extracellular side of the isolated axon. Amplifier 1 is a high-input impedance, negative capacitance amplifier, 2—high-gain differential amplifier, 3—current-to-voltage converter; 4—analogue compensator for leakage and fast and slow capacitive currents. In CC γ electrode is grounded and resistor = 3 MΩ. (b)(A) Action potential evoked by a 0.5 ms depolarizing current pulse. (b)(B) The effect of long symmetrical current pulses: the hyperpolarizing one—used to estimate the passive axonal membrane properties and the depolarizing one—used to observe the membrane rectification (Rec.). (c) Action potential recorded from in situ giant axon using microelectrode. (d) Total current recorded under voltage pulse from holding potential −70 mV to −10 mV; K⁺—potassium component, Na⁺—sodium component. (e) Voltage-dependence of sodium current recorded at various holding potentials: −1 : −60, 2 : −70 and 3 : −80 mV. The points (not shown) for curves are mean values from 5 experiments performed in control conditions. Note that at holding potential of −60 mV, about 50% of Na current is inactivated.