Heterologous expression of ion channels in Xenopus laevis (African clawed frog) oocytes
Oocytes are surgically removed from mature, female Xenopus laevis frogs under general anesthesia.
Xenopus laevis frog
Ovarian tissue contains immature and mature oocytes, as well as connective tissue from which the oocytes must be freed.

Ovarian tissue
Ovarian tissue is dissociated by gentle rocking in saline containing collagenase.

Ovarian tissue in collagenase solution
Isolated oocytes are enveloped in a tough follicle cell layer.

Isolated oocytes
Oocytes slide out of their follicle cell layers after 24-48 hours following collagenase treatment.
Manual removal of partially damaged follicle cell layers aids the process.
A second treatment with collagenase on day 2 is sometimes required to damage the layer sufficiently to allow removal.
Excessive collagenase exposure damages the oocyte itself.

Oocytes slide out of their follicle cell layers.
Intranuclear injection of oocytes with cDNA encoding the alpha and beta1 subunits of the human adult skeletal muscle sodium channel.

Intranuclear injection of oocytes with cDNA.
Two-electrode voltage clamp of oocyte expressing human skeletal muscle sodium channels.
The recording electrodes should not distort the oocyte this much, but this image shows the sites of insertion well.

Two-electrode voltage clamp.
Raw current traces from oocyte co-expressing the human adult skeletal muscle sodium channel alpha subunit and the beta1 subunit.
Several traces elicited from step-depolarizations to a range of voltages are superimposed to show the voltage dependence of the current.
Peak currents are represented by downward deflections of the current traces - this is the convention used by electrophysiologists to indicate positive charges moving into the cell (or negative charges moving out).
Note that the current magnitude increases shortly after the onset of the depolarization, and then decreases despite continuing depolarization.  This occurs as a result of inactivation of the sodium channels shortly after activation ("opening") occurs.

Approved procedure for removal of Xenopus oocytes
Last updated April 6, 2005