Voltage clamp methods

Fig. 6.21 Joint application of patch-clamp and voltage-clamp methods to the study of a single potassium channel present in the membrane of a spinal-cord neuron cultivated in the tissue culture. The values indicated before each curve are potential differences imposed on the membrane. The ion channel is either closed (C) or open (O). (A simplified drawing according to B. Hille)...

In the author s laboratory gap junction conductance between two cells is measured using the double-cell voltage-clamp method with two switch-clamp amplifiers (SEC-05, NPI Electronic, Germany) in a double whole-cell patch. The procedure is described below. 

Wilders R, Jongsma HJ Limitations of the dual voltage clamp method in assaying conductance and kinetics of gap junction channels. Biophys J 1992 63 942-953. 

Studies in Xenopus oocytes are performed with the two microelectrode voltage clamp method. For isolation of the oocytes, the toads are anesthetized using a 1 g/1 solution of 3-aminobenzoic acid ethyl ester and placed on ice. A small incision is made to retrieve sacs of oocytes and is subsequently closed with absorbable surgical suture. On waking up, the toads are placed back into the aquarium. The ovaries are cut up into small pieces and the oocytes are washed in Ca2+-free Or-2 solution (82.5 mM NaCl, 2mM KC1, ImM MgCb, 5 mM HEPES pH 7.4) and subsequently col-... 

The first measurements were made by titration of the sites associated with the conductance units by the molecules of TTX, which block the sodium conductance change. Using TTX and employing voltage-clamp methods, we were able to estimate... 

As with the conventional voltage clamp method, the patch clamp method allows experimental control of the membrane potential to characterize the voltage dependence of membrane currents. 

Subsequently, either additional ion channel studies or more sophisticated voltage-clamp methods may be used in conjunction with in vitro APD studies to assess proarrhythmia liability. In vivo models may be used before selection of the candidate drug, but use is limited due to their low-throughput nature. Prior to first in human (FIH) studies in vitro APD and in vivo APD and QT interval assessments are usually undertaken to complement the early cardiac screening data, thus establishing a dataset used to inform an integrated risk assessment as described in the ICH S7A and ICH S7B guidelines (Anon. 2001, 2005). Almost no non-clinical safety work is conducted after FIH. 

Hong, EX and Mauzerall, D., Tunable voltage clamp method application to photoelectric effects in pigmented bilayer hpid membranes, /. Electrochem. Soc., 123,1317,1976. 

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