Patch electrode

With the patch electrode voltage at 0 mV, depolarization of the cell via the whole cell electrode (-70 mV to OmV) changed the potentials of both the Pvm and the whole cell from - 70 mV to 0 mV (Fig. 4 left panel i.e. Pvm=Vwh0ie ceil Vpatch), elevated [Ca2+]c to about 800 nM, and evoked single KCa channel activity (bottom two panels). On repolarization to -70 mV, KCa channel activity ceased abruptly. In Fig. 4 (middle panel) depolarization of the whole cell from -70 mV to OmV, with the Pvm being held at -70 mV (by applying a simultaneous pulse to the patch... 

The patch electrode voltage-clamp is the method of choice to study V, alterations (Hamill et al., 1981). However, the high resistance seals required for these studies are not readily formed on mammalian sperm due both to geometric factors as well as the low compliance of the plasma membrane (Arnoult et al., 1996b). To date, recordings of whole cell currents, as is essential for monitoring of V, have not been reported in sperm, despite the heroic efforts exerted to obtain excised patches from these cells (Espinosa et al., 1998). As an alternative, has been ex-... 

Device to maintain constant voltage across membrane and to measure current flow across membrane at tip of patch electrode... 

Patch electrode filled with conducting salt solution... 

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). 

Whole-cell mode—conventional. From the initial cell-attached configuration, additional suction is applied to rupture the cell membrane, thus providing access to the intracellular space of the cell. The larger opening at the tip of the patch electrode, compared with the sharp microelectrode, provides lower resistance and thus better electrical access to the cell. Because the volume of the patch electrode is much bigger than the cell, the soluble contents of the cell will slowly be replaced by the contents of the electrode, referred to as dialyzing ... 

Free radical generation in rat CAl pyramidal neurones of organotypic shces subjected to a hypoxic-hypoglycaemic insult was temporally correlated with intracellular calcium elevation, as measured by injection of fluo-3 in individual pyramidal cells, using patch electrodes (Perez Velazquez et al. 1997). 

The silicone rubber-coated and fire-polished electrode to be used has to be filled with an ionic solution. It is very important to cleanse the material to obtain good patches. Electrodes have to be kept free from dust, and all solutions to be used have to be filtered (using a Millipore 0.2 pm filter). The compositon of the electrode solution as well as the chamber bath solution will depend on the particular experiment and on the configuration of the patch that is going to be obtained. The level of the bath solution in the recording chamber is adjusted to be as low as possible, in order to obtain small pipette capacity and, consecutively, low pipette noise. 

Filling the patch electrode If a capillary with internal filament was used to make the pipette, it can be filled simply by adding the solution... 

Initially, almost all pacemaker and ICD procedures were approached exclusively from the epicardial point of view. But with the development of a transvenous approach, either by cutdown or percutaneous techniques, now almost aU pacemaker and ICD procedures are approached on a transvenous or nonthoracotomy basis. Today, the epicardial approach is reserved for certain unique circumstances. Electrodes can be placed on the epicardium by a variety of techniques. This involves a subxiphoid incision, and limited thoracotomy, or direct application of electrodes on an exposed heart. Recently, mediastinoscopy and thoracoscopy have been used to apply permanent pacing and rate-sensing electrodes as well as patch electrodes. The transvenous approach can be performed by venous cutdown, percutaneous venous access, or a combination of the two. 

The median sternotomy is the most popular approach because it provides optimal exposure and access to the entire heart (94-96). It is used in patients undergoing an open-heart procedure who also require ICD implantation. The incision is weU tolerated and associated with much less patient discomfort. Two large patches may easily be placed extrapericardially (Fig. 4.43). Excellent exposure is achieved as the procedure is generally performed under cardiopulmonary bypass with the lungs deflated. The rate sensing leads are directly screwed to the epicardial surface. The patch electrodes are sutured to the pericardium. 

The left anterolateral thoracotomy also offers excellent exposure of the heart and left ventricle. An incision is created in the fifth intercostal space (Fig. 4.44). This approach is ideal for extrapericardial placement of a large patch electrode over the posterior surface of the left ventricle as well as a smaller patch anteriorly between the sternum and pericardium. This approach is associated with considerable postoperative pain and is its major drawback. This pain frequently results in atelectasis and transient pleural effusions. Today, a more lateral approach has been adopted that eliminates pain associated with division of the latissimus dorsi. Once again, the leads are tunneled to an abdominal pocket by use of a small chest tube or hemostat... 

Fig. 4.44 Left lateral thoracotomy with epicardial rate-sensing and patch electrodes tunneled to the subcutaneous pocket in the left upper quadrant. (From Belott PH, Reynolds DW. Permanent pacemaker and cardioverter defibrillation implantation. In Ellenbogen KA, Kay N, Wilkoff BL, eds. Clinical cardiac pacing and defibrillation, 2nd ed. Philadelphia WB Saunders, 2000, with permission.)...

Occasionally ICD systems require the placement of additional leads and/or patches to achieve adequate DFTs. An additional patch electrode may be added through a small, left anterior chest incision (Fig. 4.57). This incision is generally placed along the left inframammary skin fold. A subcutaneous pocket is developed and a supplemental patch placed. The patch is sutured to the chest wall. The proximal lead is then tunneled to the ICD. A variation on this system is the subcutaneous array developed by CPI (Fig. 4.58). The array consists of three flexible defibrillator leads that are joined at a common connector. The leads are designed to be placed subcutaneously along the contour of the chest wall. The leads fuse as a common electrode that connects to the ICD. Creating a small incision in the left lateral inframammary skin fold places the array. Three separate subcutaneous tracts are created using a blunt-tipped malleable stylet. The stylet is loaded with a sheath that is advanced down each traa. The stylet is removed and the limbs of the array are passed down each sheath. 

Chevalier P, Moncada E, Canu G, Claudel JP, Bellon C, Kirkorian G, Touboul P. Symptomatic pericardial disease associated with patch electrodes of the automatic implantable cardioverter defibrillator an underestimated complication Pacing Clin Electrophysiol 1996 19 2150-2. 

Kuhlkamp V, Domberger V, Mewis C, Seipel L. Comparison of the efficacy of a subcutaneous array electrode with a subcutaneous patch electrode, a prospective randomized study. Int J Cardiol 2001 78 247-56. 

The electrode resistance values were measured to confirm that the electrodes were electrically isolated and that the apertures were open. Fig. 6 shows a macro-patch recording obtained when a devitellinized oocyte, expressing Shaker potassium channels, was dropped onto an aperture. The ionic currents carried by a population of 80 Shaker channels were measured in response to positive step changes in membrane potential. The overall success rate for forming a gigaseal on a xenopus oocyte using a planar PDMS patch electrode was 13% (10 out of 75). This is lower than the 40 % success rate for the conventional patch electrodes with or without PDMS coating and surface treatment. 

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