Biomaterial Database

Properties of single sodium channels translated by Xenopus oocytes after injection with messenger ribonucleic acid. 1987

E Sigel

Pharmakologisches Institut der Universitaet Bern, Switzerland.

1. The properties of fast transient Na channels induced in the Xenopus laevis oocyte plasma membrane after injection of the oocyte with foreign messenger ribonucleic acid (mRNA) were investigated with the whole-cell voltage clamp and with the patch-clamp technique. 2. The time course of expression and the effect of the metabolic inhibitors actinomycin D and tunicamycin were studied. The rate of channel insertion reached a maximum only about 3 days after injection with mRNA and corresponded to the incorporation of 20 active channels/s, into a single oocyte. When applied intracellularly tunicamycin blocked the appearance of active channels nearly completely while actinomycin D added to the medium had no effect. 3. The whole-cell currents showed activation and inactivation properties reminiscent of skeletal muscle Na+ currents. The maximal peak current amplitude was 6 microA. Tetrodotoxin blocked the observed transient inward current. 50% inhibition was observed at 10 nM concentration. Veratridine depressed inactivation of the current and led to prolonged tail currents. 4. After removal of the surrounding layers of the oocyte tight seals were obtained with a patch-clamp electrode pushed on the surface membrane. Single-channel currents endogenous to the oocyte and Na+-channel currents induced by injected mRNA could be recorded. The single-channel slope conductance of the latter was 12-15 pS. Two different types of kinetic behaviour were evident from an analysis of single-channel currents and ensemble average currents. One type showed fast inactivation (tau less than 1 ms) and brief channel openings (less than 1 ms) whereas the second type was characterized by slower inactivation and a bursting behaviour. 5. When veratridine (75 microM) was present in the pipette solution the single-channel behaviour was modified in a complex manner. In addition to the channel openings with normal conductance a second open state was observed with a slope conductance of 3.5 pS. This second type of channel opening could still be recorded after return to the holding potential. Its final closure followed an exponential time course with a constant time constant of 0.5 s at -100 mV. These events probably underlie the tail currents in the whole-cell configuration. 6. The Xenopus oocyte represents a useful system for the study of the expression of channels induced by foreign mRNA, for the characterization of their single-channel behaviour and for the investigation of the action of pharmacologically active substances on these channels. This system may prove useful for the study of channels that are not accessible to patch-clamp experiments 'in situ'.

UI	MeSH Term	Description	Entries
D007473	Ion Channels	Gated, ion-selective glycoproteins that traverse membranes. The stimulus for ION CHANNEL GATING can be due to a variety of stimuli such as LIGANDS, a TRANSMEMBRANE POTENTIAL DIFFERENCE, mechanical deformation or through INTRACELLULAR SIGNALING PEPTIDES AND PROTEINS.	Membrane Channels,Ion Channel,Ionic Channel,Ionic Channels,Membrane Channel,Channel, Ion,Channel, Ionic,Channel, Membrane,Channels, Ion,Channels, Ionic,Channels, Membrane
D009865	Oocytes	Female germ cells derived from OOGONIA and termed OOCYTES when they enter MEIOSIS. The primary oocytes begin meiosis but are arrested at the diplotene state until OVULATION at PUBERTY to give rise to haploid secondary oocytes or ova (OVUM).	Ovocytes,Oocyte,Ovocyte
D003609	Dactinomycin	A compound composed of a two CYCLIC PEPTIDES attached to a phenoxazine that is derived from STREPTOMYCES parvullus. It binds to DNA and inhibits RNA synthesis (transcription), with chain elongation more sensitive than initiation, termination, or release. As a result of impaired mRNA production, protein synthesis also declines after dactinomycin therapy. (From AMA Drug Evaluations Annual, 1993, p2015)	Actinomycin,Actinomycin D,Meractinomycin,Cosmegen,Cosmegen Lyovac,Lyovac-Cosmegen,Lyovac Cosmegen,Lyovac, Cosmegen,LyovacCosmegen
D005260	Female		Females
D000200	Action Potentials	Abrupt changes in the membrane potential that sweep along the CELL MEMBRANE of excitable cells in response to excitation stimuli.	Spike Potentials,Nerve Impulses,Action Potential,Impulse, Nerve,Impulses, Nerve,Nerve Impulse,Potential, Action,Potential, Spike,Potentials, Action,Potentials, Spike,Spike Potential
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D012333	RNA, Messenger	RNA sequences that serve as templates for protein synthesis. Bacterial mRNAs are generally primary transcripts in that they do not require post-transcriptional processing. Eukaryotic mRNA is synthesized in the nucleus and must be exported to the cytoplasm for translation. Most eukaryotic mRNAs have a sequence of polyadenylic acid at the 3' end, referred to as the poly(A) tail. The function of this tail is not known for certain, but it may play a role in the export of mature mRNA from the nucleus as well as in helping stabilize some mRNA molecules by retarding their degradation in the cytoplasm.	Messenger RNA,Messenger RNA, Polyadenylated,Poly(A) Tail,Poly(A)+ RNA,Poly(A)+ mRNA,RNA, Messenger, Polyadenylated,RNA, Polyadenylated,mRNA,mRNA, Non-Polyadenylated,mRNA, Polyadenylated,Non-Polyadenylated mRNA,Poly(A) RNA,Polyadenylated mRNA,Non Polyadenylated mRNA,Polyadenylated Messenger RNA,Polyadenylated RNA,RNA, Polyadenylated Messenger,mRNA, Non Polyadenylated
D012964	Sodium	A member of the alkali group of metals. It has the atomic symbol Na, atomic number 11, and atomic weight 23.	Sodium Ion Level,Sodium-23,Ion Level, Sodium,Level, Sodium Ion,Sodium 23
D013779	Tetrodotoxin	An aminoperhydroquinazoline poison found mainly in the liver and ovaries of fishes in the order TETRAODONTIFORMES, which are eaten. The toxin causes paresthesia and paralysis through interference with neuromuscular conduction.	Fugu Toxin,Tarichatoxin,Tetradotoxin,Toxin, Fugu
D013997	Time Factors	Elements of limited time intervals, contributing to particular results or situations.	Time Series,Factor, Time,Time Factor