Voltage clamp technique

Shattock M. J. and Matsuura, H. (1993). Measurement of Na -K pump current in isolated rabbit ventricular myocytes using the whole-cell voltage-clamp technique. Inhibition of the pump by oxidant stress. Circ. Res. 72, 91-101. 

The opening of masses of ion channels in nematode muscle membranes may be detected using the two-microelectrode voltage-clamp technique. In contrast, the opening of single ion channels may be recorded using the vesicle preparation and patch-clamp technique. These techniques are both described below. 

This problem of overlapping expression of sodium channel isoforms has recently begun to be addressed using cloned channels heterologously expressed individually in Xenopus laevis oocytes with voltage-clamp techniques and the picture that is emerging is that there are substantial differences in the sensitivity of mammalian sodium channel isoforms to the pyrethroids. 

Cultured embryonic chick heart cells often form coupled cell pairs or aggregates which may be studied using the double-cell voltage-clamp technique. In the following an isolation and culture protocol is given as used in the author s laboratory. Besides this, other protocols may also suit. 

Daut J The passive electrical properties of guinea pig ventricular muscle as examined with a voltage clamp technique. J Physiol (bond) 1982 330 221-242. 

Apart from HCN channels, genistein (42) also acted on other types of channels present in cardiac cells. Chiang et al. [306] examined the impact of this isoflavone on the L-type calcium and cAMP- dependent chloride currents in guinea pig ventricular myocytes. Using the voltage-clamp technique they found that genistein (42) reversibly inhibited L-type calcium currents in a dose-dependent manner. Surprisingly daidzein (40), which was ineffective with respect to many other channel types, also decreased L-type calcium currents in myocytes. Opposite to calcium currents, the cAMP-dependent... 

However, the ionic currents measured using the voltage clamp technique were the result of fluxes through an ensemble of membrane channels. Until the 1970s, it had only been possible to study ion channels as macroscopic cur-... 

Barros etal. (1986) studied the effect of TRH on cultured GH3 rat anterior pituitary cells using the wholecell voltage clamp technique. 

The origin of these modifications has been studied using the voltage-clamp technique. 

The most precise measure of this interaction requires the voltage clamp technique, but a qualitative indication can be obtained using conventional intracellular potential recording. 

Voltage-clamping techniques, which hold the electrical potential across the neuronal membrane constant, while still allowing for the transmural flux of ions, have provided detailed analyses of the rates at which various ions cross the membrane and the kinetics of ion channel activation and inactivation. Specific information about a given anion or cation can be obtained by altering the ionic composition of the bathing medium (Hodgkin and Huxley, 1952 also see Aidley, 1971). 

Figure 16.2 Illustration of the squid giant axon action potential and its dependence on external Na+. The resting membrane potential (Em) is about -60 mV. Following stimulation (S), the initial Na+-dependent depolarization phase of the action potential that rises above 0 mV (overshoot) is gradually reduced in amplitude and delayed in time with reduction in extracellular Na+. Similar experiments were originally conducted by Hodgkin, Huxley, and Katz in the 1930s/1950s using the voltage clamp technique (Section 16.5.1.1).

This technique allows the study of single-ion channels as well as whole-cell ion channel currents. Essentially, the patch-clamp technique is an improved and refined version of the voltage-clamp technique. It requires a low electrical noise borosiUcate glass electrode, also known as a patch electrode or patch pipette, with a relatively large tip (>1 pm) that has a smooth surface rather than a sharp tip as with the conventional microelectrodes. This is a major difference between the patch electrode and the sharp electrode used to impale cells directly through the cell membrane (Figure 16.20). 

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