Voltage clamp experiments

Eisner The problem with this sort of experiment is that with the right sort of voltage clamp experiment you can show evidence that CICR, under some circumstances, can amplify the signal. The question is, does it do it normally. 

This work was supported by NSF Grant No. DAR-8003523. Early work on the toxins was supported by the New Hampshire Water Resources Research Center of the University of New Hampshire, Grant No. AO-47NH, from the Office of Water Research and Technology, United States Department of the Interior as authorized under the Water Research and Development Act of 1978, Public Law 95-467. We also thank Dr. William J. Adelman, Jr., NINCDS, Woods Hole, for performing the voltage-clamp experiments Kurt Auger for superior work in biochemistry and Toshinori Hoshi for studies on the crayfish axons. 

Due to certain behaviors anomalous to the HH model obtained from some preparations in voltage clamp experiments (18,19), a number of models have been proposed whereby Na+ activation and inactivation are coupled into a multistate sequence rather than proceeding independently as suggested by HH m h dynamics. For example, consider the following kinetic scheme suggested by Goldman and Hahin (20)... 

A hypothesis has been offered to explain muscle hyperexcitability in response to suxamethonium (75). Voltage clamp experiments on alpha subunits of human muscle... 

Spruston I think it is possible to work at 37 °C we now do all our work at this temperature. Returning to slow inactivation, another important point is to distinguish between the rate of entry into the inactivated state and the rate of recovery from it. We find that in hippocampal neurons, slow inactivation is actually slow recovery from inactivation as opposed to slow entry. This is particularly important, because the most efficient way to drive channels into that state is with repetitive brief depolarizations in voltage clamp experiments. In the... 

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. 

The voltage clamp experiments outlined above permit recording of opening and closing of many sodium channels contained in a large nerve membrane area. A question arises as to how individual... 

There are several reports which indicate that small organic cations can naaintain excitability of squid giant axons in sodium-free solutions [24]. Binstock and Lecar [25] carried out voltage-clamp experiments using NH/ and found that NH4 permeates both Na and K channels. 

Yanagihara, K., A. Noma, and H. Irisawa (1980). Reconstruction of sino-atrial node pacemaker potential based on the voltage clamp experiments. Japan. J. Physiol. 30,841-857. 

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... 

The spectral analysis of fluctuations yields also valuable information, and it can be used to test the validity of kinetic schemes describing the transitions between different channel states. In Ranvier nodes the component of the sodium current fluctuations which corresponds to the sodium inactivation process observed in voltage-clamp experiments is much larger than expected from a simple Hodgkin-Huxley scheme with statistically independent activation and inactivation processes. This finding provides a strong argument in favour of the hypothesis that the inactivation process is at least partially sequential to the activation process. 

Unfortunately, voltage-clamp experiments show that the time constants describing the relaxation of sodium (or potassium) currents do not fullfill this requirement (with the exception of the inactivation time constant, discussed later). According to the Hodgkin-Huxley equations (18), the relaxation of potassium currents is described by four time constants with values in the ratio of 1 2 3 4. Likewise, the rising phase of sodium currents contains approximately three exponentials, with time constants in the ratio of 1 2 3. 

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