The Kir3.1 K+ channel participates in heart rate control and neuronal excitability through G‐protein and lipid signaling pathways. Expression in Escherichia coli has been achieved by replacing three fourths of the transmembrane pore with the pore of a prokaryotic Kir channel, leaving the cytoplasmic pore and membrane interfacial regions of Kir3.1 origin. Two structures were determined at 2.2 Å. The selectivity filter is identical to the Streptomyces lividans K+ channel within error of measurement (r.m.s.d.<0.2 Å), suggesting that K+ selectivity requires extreme conservation of three‐dimensional structure. Multiple K+ ions reside within the pore and help to explain voltage‐dependent Mg2+ and polyamine blockade and strong rectification. Two constrictions, at the inner helix bundle and at the apex of the cytoplasmic pore, may function as gates: in one structure the apex is open and in the other, it is closed. Gating of the apex is mediated by rigid‐body movements of the cytoplasmic pore subunits. Phosphatidylinositol 4,5‐biphosphate‐interacting residues suggest a possible mechanism by which the signaling lipid regulates the cytoplasmic pore.

Inward rectifier K(+) channels govern the resting membrane voltage in many cells. Regulation of these ion channels via G protein-coupled receptor signaling underlies the control of heart rate and the actions of neurotransmitters in the central nervous system. We have determined the protein structure formed by the intracellular N- and C termini of the G protein-gated inward rectifier K(+) channel GIRK1 at 1.8 A resolution. A cytoplasmic pore, conserved among inward rectifier K(+) channels, extends the ion pathway to 60 A, nearly twice the length of a canonical transmembrane K(+) channel. The cytoplasmic pore is lined by acidic and hydrophobic amino acids, creating a favorable environment for polyamines, which block the pore. These results explain in structural and chemical terms the basis of inward rectification, and they also have implications for G protein regulation of GIRK channels.

In an RF-discharge methane plasma, the dissociation rate of CH4 in collisions with electrons has been measured using a laser absorption technique. The measured rate increases as the RF power increases and as the gas pressure decreases. The electron energy distribution function f( epsilon ) and the electron density ne have also been measured by a heated electrical probe. The measured f( epsilon ) is quite different from the Maxwellian distribution and rather close to the Druyvesteynian distribution. The dissociation rate constant deduced from f( epsilon ) and the reported cross-section when multiplied by the measured ne is consistent with the results of the laser absorption method. Based on these measurements a modelling of the plasma has been performed using a set of rate equations for CH4 and the various neutral and ionic species produced in the plasma. The calculated degree of dissociation for CH4 in the plasma agrees well with the measured results. The most abundant neutral radical in the plasma predicted by the model is CH3, while CH5 + is the most abundant ionic species.