Established Protocols for cRNA Expression and Voltage-Clamp Characterization of the P2X7 Receptor in Xenopus laevis Oocytes.

P2X7 receptors (P2X7Rs) are fast ATP4--gated ion channels that, like other members of the P2X receptor family, function as homotrimers. A high-resolution cryo-EM structure of the full-length rat P2X7R is available. Using voltage-clamp experiments in Xenopus laevis oocytes, even the earliest steps of P2X7R activation can be quantitatively recorded in the millisecond range. Site-directed mutagenesis combined with voltage-clamp recordings can reveal residues and domains of the P2X7R involved in ATP4- binding, gating (i.e., opening and closing of the channel pore) and ion selectivity. We present here proven voltage-clamp protocols that take into account requirements that are important at the levels of cDNA and vector sequences, cRNA synthesis, and Xenopus laevis oocyte isolation for reliable results.

The P2X7 carboxyl tail is a regulatory module of P2X7 receptor channel activity.

P2X(7) receptors are ATP-gated cation channels composed of three identical subunits, each having intracellular amino and carboxyl termini and two transmembrane segments connected by a large ectodomain. Within the P2X family, P2X(7) subunits are unique in possessing an extended carboxyl tail. We expressed the human P2X(7) subunit as two complementary fragments, a carboxyl tail-truncated receptor channel core (residues 1-436 or 1-505) and a tail extension (residues 434-595) in Xenopus laevis oocytes. P2X(7) channel core subunits efficiently assembled as homotrimers that appeared abundantly at the oocyte surface, yet produced only approximately 5% of the full-length P2X(7) receptor current. Co-assembly of channel core subunits with full-length P2X(7) subunits inhibited channel current, indicating that the lack of a single carboxyl tail domain is dominant-negative for P2X(7) receptor activity. Co-expression of the tail extension as a discrete protein increased ATP-gated current amplitudes of P2X(7) channel cores 10-20-fold, fully reconstituting the wild type electrophysiological phenotype of the P2X(7) receptor. Chemical cross-linking revealed that the discrete tail extension bound with unity stoichiometry to the carboxyl tail of the P2X(7) channel core. We conclude that a non-covalent association of crucial functional importance exists between the carboxyl tail of the channel core and the tail extension. Using a slightly shorter P2X(7) subunit core and subfragments of the tail extension, this association could be narrowed down to include residues 409-436 and 434-494 of the split receptor. Together, these results identify the tail extension as a regulatory gating module, potentially making P2X(7) channel gating sensitive to intracellular regulation.

Hirudin as alternative anticoagulant--a historical review.

Advances in separation techniques and biotechnology have contributed to the development of anticoagulant agents from hematophagous animals. The most potent known natural thrombin inhibitor from blood-sucking leeches ( Hirudo medicinalis), hirudin has served as a standard for designing the natural coagulation inhibitors as an anticoagulant drug. The search for the development of hirudin from leech extract to genetically engineered products as an alternative anticoagulant has been resumed. The pharmacological profiling of the isolated thrombin inhibitor has shown that native hirudin is an antithrombotic agent of high quality. However, its clinical use has remained limited, because the substance has not been available in adequate amounts. The progress in molecular biology has stimulated the interest in the structure and function of hirudin. This development resulted in the production of recombinant hirudins (r-hirudins) through gene technology. The biological properties of hirudin combined with the ready availability of recombinant forms make the specific thrombin inhibitor well-suited for use as an antithrombotic drug. Its use should lead to a decisive progress in the management of thromboembolic diseases of both arterial and venous origin. Clinical trials, especially in diseases in which thrombin plays a crucial role, are in progress.