Voltage-clamp experiments, effects

Effects of pyrethroid molecules on isolated axons (voltage-clamp experiments). 

The method used to reconstruct nerve behaviour derives directly from that originally proposed by Hodgkin and Huxley (18) for squid axons. The parameters used in these equations have been taken from earlier experiments on isolated cockroach axons (19-20). To reproduce the effects of the insecticide, a set of new equations, the "p" equations, have been derived from the above voltage-clamp experiments. The steady-state values of p as well as the values of the time constants used in the reconstructions are illustrated in Fig.5. It is assumed that activation of the slow channels is a first order process and that these channels do not inactivate. 

Voltage clamp experiments using identified neurons, dorsal unpaired median (DUM) neurons from the terminal abdominal ganglion of P. americana, demonstrated that DCJW inhibited the peak Na+ current with an IC50 of 28 nM [38]. DCJW (7) (100 mv[) induced a hyperpolarization of DUM neurons associated with block of background Na channels involved in maintenance of the resting potential. While the peak Na+ current was inhibited, DCJW had no effect on either activation or inactivation kinetics (Fig. 29.4.13). Zhao et al. (2005) similarly... 

Hescheler J, Delpiano MA, Acker H, Pietraschka F. Ionic currents on type-I cells of the rabbit carotid body measured by voltage-clamp experiments and the effect of hypoxia. Brain Res 1989 486(l) 79-88. 

Schlatter E (1993) Effect of various diuretics on membrane voltage of macula densa cells. Whole-cell patch-clamp experiments. Pfliigers Arch Eur J Physiol 423 74-77... 

In TTX experiments the steady-state potassium currents for large depolarizations were often slightly increased by pressure. However, as judged by the current jump following the end of the voltage clamp pulses, this effect appears to arise from a smaller potassium accumulation in the outer Schwann space (20) due to the slower development of the potassium currents. Thus, increasing pressure from 1 atm to 612 atm has a very small, if any, effect on the maximum potassium conductance, g. A possible small shift of the potassium activation curve, n (V), (less than 10 mV, in the depolarizing direction, at 612 atm) was observed but could not be analyzed in detail because our current records were too brief for a correct estimation of steady-state conductances at small depolarizations. 

Taken together, the limited experiments conducted using neuronal cell cultures illustrate a distinct difference in the way that pyrethroids modify ion conductance and subsequent neurotransmitter release under resting and depolarized conditions. Continued efforts utilizing recent new tools like automated patch-clamp systems and MEAs to assess the effects of pyrethroids on the kinetics and voltage-dependent gating of ion channels in primary cultures or transfected cells is likely to provide new insight into the neurotoxicity of pyrethroids [79, 82]. 

Our main result is that the nanotube can be manipulated by the gate voltage, which determines its deformation and stress, and modifies the eigen-modes. Though the eigenmodes of nanotube ropes have been measured in Ref. [12] four years ago, the strain dependence of the eigenmodes was only recently reported in Ref. [15]. ft demonstrates this effect for singly-clamped multi-wall carbon nanotubes. We expect that our predictions will soon be tested in experiments on doubly-clamped SWNTs. 

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