Expression of functional sodium channels in stage II-III Xenopus oocytes.

We have injected mRNA from rabbit brain into stage II-III Xenopus oocytes to determine whether they will translate exogenous RNA and incorporate functional ion channels into the membrane. Our results show that 48 h after RNA injection, functional voltage-dependent Na channels are present at sufficient densities to allow quantitative electrophysiological recording. The smaller oocytes have at least 2 experimental advantages over the stage V-VI oocytes normally used for electrophysiological experiments: (1) the smaller membrane capacitance (approximately 5-fold) allows a faster settling time following a voltage step and a more detailed kinetic analysis of membrane currents than was previously possible with the 2-microelectrode technique, and (2) roughly 8-fold less RNA is needed for each injection. Thus, the stage II-III Xenopus oocyte is a suitable preparation for the study of ion channels.