Electrophoretic Mobility of Red Cells and Their Ghosts as Observed with Improved Apparatus^*

The two principal conclusions reached in the investigations with the ordinary microscope and the Abramson horizontal electrophoresis cell (Abramson, Furch-gott & Ponder, 1939; Furchgott & Ponder, 1941) were that the isoelectric point of the haemolysed red cell is in the neighbourhood of pH 2-0, and that ghosts, regardless of the way in which they are prepared (with the exception of the ghost prepared by lysis in CO₂-saturated hypotonic saline), have the same mobility as that of the red cells from which they are prepared. The first conclusion can be confirmed by the improved methods used here, but the second is an oversimplification.

The construction of the new cell (Fig. 1) is based on that of a vertical cell already described (Ponder, 1951). It differs from the latter in that it has removable electrodes and that the objects (red cells and ghosts) are seen by phase contrast.

The flat rectangular cell C and the tubes which lead to it are held rigidly on a square frame F of glass rod. Two 3-way stopcocks and S₂ lead to the female parts of the ground joints of the electrodes E₁ and E₂, into which the removable non-polarizable electrodes fit as male parts. Each electrode has a short horizontal part and a short vertical part. The end of the horizontal part which fits into the ground joint is closed with a plate of fritted glass about 1 mm. thick, into which some plaster of Paris is rubbed. The end of the vertical part is closed with a snugly fitting rubber stopper through which a short rod of copper passes. A piece of fine insulated wire, ending in a lug, attaches the copper rod to one of the two terminals of the electrical circuit; by detaching the lug from the terminal, the electrode can be detached from the electrical circuit, and it can also be detached from the electrophoresis cell at the ground joint. The cell is filled by suction through a rubber tube attached at A and empties at B. A 2-way stopcock S₃ has been introduced above ; when S₃ is closed, the column of fluid below it behaves as if it were a closed column, almost regardless of the positions of S₁ and S₂.

The frame F is mounted on a metal plate about 1 mm. thick, with a large central aperture through which a long focus phase condenser can project. The plate is clamped, in such a way that it can be removed and returned to exactly the same position, to the square stage of a microscope which is arranged with its stage vertical and its body tube horizontal. The stage and the substage of the standard microscope have to be altered in order that the long-focus phase condenser can be brought close enough to the back of the electrophoresis cell.* The optical system consists of an 8 mm. phase objective (× 21), a long-focus phase condenser (Bausch and Lomb), and a 25 ^× eyepiece which carries an eyepiece micrometer disk ruled in squares, each covering about 100 μ.². The light source is a 100 W. projection lamp situated several feet from the electrophoresis cell. A large water jacket and a green filter are inserted in the light path. The electrical circuit consists of a few 45 V. dry batteries, a reversing switch, a milliammeter, and a resistance in series with the cell. The resistance of the cell, when filled with 1 % NaCl, is about 15 ×10³ Ω.

The cell, which should be cleaned with soapy water followed by many rinses of distilled water, is filled in the following way. The electrodes are first prepared by filling them with saturated CuSO₄, inserting the rubber stoppers with their copper rods, rinsing their outsides with water, and applying a thin layer of stopcock grease to their ground surfaces. The cell, on its frame which is permanently attached to the plate, is removed by unclamping the plate from the microscope stage. The rubber tube leading from A is attached to a Mariotte bottle containing saline or buffer. With the stopcocks S₁ and S₂ in position 1 (see inset of Fig. 2), the stopcock S₃ is opened. This fills the female part of the upper electrode; S₃ is closed, and the male part of the upper electrode is inserted into the upper ground joint. Next 5₁ and S₂ are turned into position 2 ; S₃ is opened ; the cell and the female part of the lower electrode then fill with saline or buffer. S₃ is again closed, and the male part of the lower electrode is inserted into the lower ground joint. S₈ is now turned into position 3; S₃ is opened, and the tube below S₂ is filled. 5₃ is closed again, and 5_X and 5₂ are turned into position 4. This procedure fills the cell and connects it with the electrodes. There must be no air bubbles.

The cell is returned to the microscope stage, to which it is clamped. To fill the cell with a suspension of red cells or of ghosts, it is first emptied by turning S₁ and S₂ into position 3 and opening S₃. The suspension can then be drawn up, from a vessel placed below B, by applying suction to the rubber tube attached to A. The suspension should be drawn up above S₃, which is then closed. S₁ and S₂ are turned into position 4. After a few minutes, during which currents in the fluid become negligible, the cell is ready for the making of mobility measurements at the stationary levels. The distance over which a cell or ghost moves during a short period of time (usually 10 sec.) is observed, first with the current flowing in one direction and then in the other, and the small movement due to gravity or to small systematic drifts (liable to occur in vertical cells) is added or subtracted. The time is much more conveniently measured by the beats of a metronome than with a stopwatch. If large systematic drifts develop, the cell should be emptied and refilled; this takes less than a minute to do. After some hours of work, drifts attributable to diffusion, etc., in the neighbourhood of the electrodes develop; the electrodes should therefore be freshly prepared before the cell is filled at the beginning of each day’s work.

Attention should be called to several points. (1) The electrophoresis cell, including the side-tubes which lead to the electrodes, must be filled with the medium in which the cells are suspended. This may be saline or a variety of isotonic buffers, but when the medium is changed the entire filling operation must be carried out anew. If the side-tubes leading to the electrodes are filled with saline, for example, while the cell and the vertical tubes leading to it are filled with a suspension of red cells or ghosts in buffer, the system will soon become unstable and the suspension will begin to stream. (2) Care must be taken not to introduce small air bubbles into suspensions of cells or ghosts, as is easily done when centrifuged material is resuspended by shaking. The upward movement of these small bubbles or of ghosts to which they have stuck is a serious source of instability in the vertical cell. (3) When making measurements of the mobility of ghosts, which are inconspicuous objects even when seen with phase contrast, special care should be taken to be sure that the ghost is in one of the stationary levels. Ghosts tend to move out of these levels more than red cells do, and the best measurements of the mobility of ghosts are those in which the ghost is seen edgewise; when seen edgewise, it almost certainly lies at the stationary level upon which the objective is focused.

The Antweiler microelectrophoresis apparatus (Antweiler, 1952) is essentially a Tiselius apparatus with a Philpot-Svensson attachment, but capable of giving electrophoretic patterns of the proteins in serum, etc., with very small quantities (0·1 ml.) of material and very rapidly (within 10 min.). The light beam which passes through an observation channel is deflected in proportion to the refractive index and therefore to the concentration of the protein in the fluid in the channel, and as the components move under an applied e.m.f., a pattern develops which can be seen with the Philpot-Svensson attachment. If the channel is filled with a suspension of red cells or their ghosts, these may also move when an e.m.f. is applied, and the position of the boundary between the moving objects, e.g. red cells, and the surrounding medium can be observed with the Philpot-Svensson attachment used without its cylindrical lens. Instead, the channel is observed directly, and the rate of movement, under an applied e.m.f., of the advancing front of the columns of red cells, etc., can either be photographed or measured with an eyepiece micrometer.

The necessity for knowing the volume concentration of each suspension of ghosts, so that the rate of movement of the boundary can be compared with that of a red cell suspension of the same volume concentration, is a real objection to the method. In the case of suspensions of some kinds of ghost, e.g. those produced by saponin, the volume concentration is very difficult to determine by centrifuging, although determinations by conductivity methods are still possible ; a less specific, although still important objection is, however, that the electrophoresis cell has to be cleaned and dried before each determination is made. This is very time consuming.

These are shown in Table 1 and Fig. 2. Apart from showing a general agreement between the relative mobilities obtained with the new vertical cell and with the moving boundary method, the values in Table 1, which are the ratios of the mobility of the object under consideration to the mobility of fresh human red cells under comparable conditions of voltage drop, pH, volume concentration, etc., show that:

• (a) The mobility of red cells which have been stored at 4°C. for long periods of time is less than that of fresh red cells.

• (b) Fresh watery ghosts have a considerably higher mobility than the red cells from which they are prepared, but the difference decreases with the length of time during which the ghosts are stored at 4°C.

• (c) The fragmentation of washed human red cells by heat (53°C. for 5 min.) gives fragments which have a higher mobility than that of unheated red cells.

• (d) Ghosts made by freezing and thawing or by haemolysis by saponin have substantially the same mobility as the red cells from which they are prepared ; this is the conclusion reached by Abramson et al. (1939). On the other hand, ghosts prepared by the CO₂ method have a mobility much less than that of the red cells from which they are prepared; this is the conclusion reached by Furchgott & Ponder (1941), except that the reduction in mobility observed here is somewhat larger (a reduction to 0·71 in the red cell mobility instead of the reduction formerly observed, which was 0·82 of the red cell mobility).

These results show that the mobility of ghosts is often different from that of the intact cell. It may sometimes be the same, especially when the ghost is relatively well haemoglobinized, but the mobility is a function of the method by means of which the ghost is prepared and of the time which has elapsed after lysis of the cell. Leaching-out of material from certain types of ghost (Waugh & Schmitt, 1940) may be responsible for the time effects.

There is little doubt that the isoelectric point of the watery ghost is as low as pH 2·0 or even lower. Fig. 2 shows the pH-mobility curve found by Furchgott & Ponder in 1941 and also the curve obtained with the new vertical cell. In the case of the former (dotted in Fig. 2) the pH was controlled by a variety of buffers with ionic strength 0·172, whereas in the case of the latter, Michaelis’s universal buffer (acetate and veronal), which has the same ionic strength at all pH’s between 2·6 and 9·6, was used. The two pH-mobility curves are not identical but are very similar, and the isoelectric point of the ghost, regardless of whether it is the ghost of a red cell haemolysed at a low pH or a watery ghost suspended in a medium of low pH (as in the case of the observations with the vertical electrophoresis cell) is certainly situated at a pH of 2 or even less.

Two new techniques for measuring the electrophoretic mobility of red cells and ghosts are described. In the first, the mobilities are measured in a vertical electrophoresis cell in which they are seen by phase contrast. This enables mobilities to be measured even when ghosts contain so little Hb as to be invisible with the ordinary microscope. The second method uses an Antweiler electrophoresis apparatus to give measurements of the mobility of moving boundaries between columns of red cells or ghosts and the suspension medium.

It can be shown by these methods that the usual statement that the mobilities of ghosts are the same as those of the red cells is an over-simplification. The mobilities, under comparable conditions, are more generally dependent on the method used to prepare the ghosts and on the time which has elapsed after lysis.

The statement that the isoelectric point of watery ghosts is as low as pH 2.0 or even less is confirmed, as is also the general shape of the pH-mobility dependence.