Time course of the induction of acetylcholine receptors in Xenopus oocytes injected with mRNA from Electrophorus electricus electroplax.

mRNA from the electroplax of adult Electrophorus electricus was injected into Xenopus oocytes. At various times after injection, the induction of the nicotinic acetylcholine (ACh) receptor in the oocyte membrane was studied electrophysiologically using a two-electrode current clamp. When the ACh sensitivity was induced, membrane potential and conductance rapidly rose from the resting value to their peaks and slowly fell (desensitization) in response to bath-applied 0.1 mM ACh. It took a latency period of 8 +/- 2.6 h (n = 10) from mRNA injection to the first appearance of the ACh sensitivity. During about 10 h incubation after the onset, the increasing speed in the peak of ACh-induced conductance change with incubation time was slow at first and accelerated later. The speed was then decelerated until the induction stages of 60 h. Apparent desensitization properties of the induced receptors changed with an increase of incubation time. During the early induction stages, the conductance decline after its peak followed two exponentials in a minute time region of ACh application: an early slow and a late fast one. The rate of decline in the late fast component slowed down markedly with incubation time. Finally the desensitization followed a single exponential.