Inward rectification of the IRK1 K+ channel reconstituted in lipid bilayers.

Inwardly rectifying potassium (K+) channels (IRK1) were incorporated into lipid bilayers to test the relative contributions of various mechanisms to inward rectification. IRK1 channels were expressed in Xenopus laevis oocytes and oocyte membrane vesicles containing the channels were fused with lipid bilayers. The major properties of the IRK1 channel were similar whether measured in the oocyte membrane or lipid bilayer; the single channel conductance was 21 pS in 140 mM symmetrical [K+] and varied as a square root of external [K+]. Importantly, IRK1 channels display voltage-dependent inward rectification in the absence of divalent ions or charged regulators such as spermine, indicating that they possess an intrinsic rectification mechanism. Although rectification was significantly increased by either Mg2+ or spermine added to the cytoplasmic face of the channel, their effects could not be explained by simple block of the open pore. The Hille and Schwartz (1978) model, originally proposed to explain inward rectification by singly charged blocking particles, cannot be used to explain rectification by multiply charged blocking particles. As an alternative, we propose that in addition to a slow gating mechanism producing long lasting open and closed states, there is a distinct, intrinsic fast gating process amplified by cytoplasmic Mg2+ and/or polyamine binding to the channel.

Nonselective and G betagamma-insensitive weaver K+ channels.

Homozygous weaver mice are profoundly ataxic because of the loss of granule cell neurons during cerebellar development. This granule cell loss appears to be caused by a genetic defect in the pore region (Gly156-->Ser) of the heterotrimeric guanine nucleotide-binding protein (G protein)-gated inwardly rectifying potassium (K+) channel subunit (GIRK2). A related subunit, GIRK1, associates with GIRK2 to constitute a neuronal G protein-gated inward rectifier K+ channel. The weaver allele of the GIRK2 subunit (wvGIRK2) caused loss of K+ selectivity when expressed either as wvGIRK2 homomultimers or as GIRK1-wvGIRK2 heteromultimers. The mutation also let to loss of sensitivity to G protein betagamma dimers. Expression of wvGIRK2 subunits let to increased cell death, presumably as a result of basal nonselective channel opening.

The K+ channel inward rectifier subunits form a channel similar to neuronal G protein-gated K+ channel.

G protein-activated inwardly rectifying K+ channel subunits GIRK1 (Kir 3.1), GIRK2 (Kir 3.2), and CIR (Kir 3.4) were expressed individually or in combination in Xenopus oocytes and CHO cells. GIRK1 coexpressed with CIR or GIRK2, produced currents up to 10-fold larger than any of the subunits expressed alone. No such clear synergistic effects were observed upon coexpression of CIR/GIRK2 under the same conditions. Coexpression of G protein beta gamma (G beta 1 gamma 2) increased the current through GIRK1/GIRK2 and GIRK2 channels. G beta gamma subunits purified from bovine brain, increased channel activity 50-1000-fold in patches from cells expressing GIRK1/GIRK2 or GIRK2 alone. The single GIRK1/GIRK2 channels resembled previously described neuronal G protein-gated K+ channels. In contrast, single GIRK2 channels were short-lived and unlike any previously described neuronal K+ channel. We propose that some neuronal G protein-activated inward rectifier K+ channels may be formed by a GIRK1/GIRK2 heteromultimer and that G beta gamma activation may involve both subunits.

The cardiac inward rectifier K+ channel subunit, CIR, does not comprise the ATP-sensitive K+ channel, IKATP.

Cardiac IKACh is comprised of two inwardly rectifying K+ channel subunits, CIR and GIRK1 (Krapivinsky, G., Gordon, E. G., Wickman, K., Velimirovic, B., Krapivinsky, L., and Clapham, D. E. (1995) Nature 374, 135-141). A cardiac protein virtually identical to CIR, termed rcKATP-1 (Ashford, M. L. J., Bond, C. T., Blair, T. A., and Adelman, J. P. (1994) Nature 370, 456-459), was reported to form an ATP-sensitive inwardly rectifying K+ channel, IKATP. We attempted to determine whether CIR alone or together with an unknown protein(s) participated in the formation of cardiac IKATP. Expression of CIR in insect, oocyte, and mammalian cell systems did not increase the appearance of ATP-sensitive currents, but rather gave rise to unique strongly inwardly rectifying, G protein-regulated K+ currents. CIR protein is found exclusively in atria, in contrast to the predominance of IKATP functional activity in ventricle. Also, CIR was completely depleted from heart membrane after immunodepletion of GIRK1. We conclude that CIR/rcKATP-1 is not a subunit of cardiac IKATP and that GIRK1 is the only channel protein coassociating with CIR in heart.

The G-protein-gated atrial K+ channel IKACh is a heteromultimer of two inwardly rectifying K(+)-channel proteins.

Heart rate is slowed in part by acetylcholine-dependent activation of a cardiac potassium (K+) channel, IKACh. Activated muscarinic receptors stimulate IKACh via the G-protein beta gamma-subunits. It has been assumed that the inwardly rectifying K(+)-channel gene, GIRK1, alone encodes IKACh. It is now shown that IKACh is a heteromultimer of two distinct inwardly rectifying K(+)-channel subunits, GIRK1 and a newly cloned member of the family, CIR.

Opposing mechanisms of regulation of a G-protein-coupled inward rectifier K+ channel in rat brain neurons.

In locus coeruleus neurons, substance P (SP) suppresses an inwardly rectifying K+ current via a pertussis toxin-insensitive guanine nucleotide binding protein (G protein; GnonPTX), whereas somatostatin (SOM) or [Met]enkephalin (MENK) enhances it via a pertussis toxin-sensitive G protein (GPTX). The interaction of the SP and the SOM (or MENK) effects was studied in cultured locus coeruleus neurons. In neurons loaded with guanosine 5'-[gamma-thio]triphosphate (GTP[gamma S]), application of SOM (or MENK) evoked a persistent increase in the inward rectifier K+ conductance. A subsequent application of SP suppressed this conductance to a level less than that before the SOM (or MENK) application; the final conductance level was independent of the magnitude of the SOM (or MENK) response. This suppression by SP was persistent, and a subsequent SOM (or MENK) application did not reverse it. When SP was applied to GTP[gamma S]-loaded cells first, subsequent SOM elicited only a small response. In GTP-loaded neurons, application of SP temporarily suppressed the subsequent SOM- (or MENK)-induced conductance increase. These results suggest that the same inward rectifier molecule that responds to an opening signal from GPTX also responds to a closing signal from GnonPTX. The closing signal is stronger than the opening signal.

The role of arachidonic acid metabolism in somatostatin and substance P effects on inward rectifier K conductance in rat brain neurons.

Somatostatin enhances an inward rectifier K conductance in cultured locus coeruleus neurons, while substance P reduces an inward rectifier K conductance in cultured nucleus basalis and locus coeruleus neurons. The role of arachidonic acid metabolites in these responses was studied. The somatostatin-induced response was reduced by phospholipase A2 inhibitors, non-specific lipoxygenase inhibitors and specific 5-lipoxygenase inhibitors. A cyclooxygenase inhibitor and a 12-lipoxygenase inhibitor had no effect. 5(S)-HPETE occasionally increased the K conductance, but failed to occlude the somatostatin response. The substance P response was suppressed by a 5-lipoxygenase inhibitor but not by a 12-lipoxygenase inhibitor. These results suggest that the 5-lipoxygenase pathway is not a specific messenger of either one of these responses, but that it plays a more general role in maintaining or enhancing the effectiveness of both somatostatin and substance P responses.

Two signal transduction mechanisms of substance P-induced depolarization in locus coeruleus neurons.

Effects of substance P on cultured neurons of the locus coeruleus of the rat were studied using the whole-cell patch clamp technique. In some cells substance P produced a decrease in a K conductance which showed an inwardly rectifying property. In other cells substance P produced an initial inward current which was accompanied by a conductance increase. The rest of the cells showed responses which were mixtures of the above two responses. The measurement of the reversal potential of the initial inward current after suppressing the voltage-gated Ca and K conductances suggests that it is caused by an increase in a non-selective ionic conductance. In cells loaded with 260 microM GTP gamma S, application of substance P produced an irreversible reduction of the K conductance, while the initial inward current could still be recorded, suggesting that the former is mediated by a G protein, whereas the latter may be activated by a different signal transduction mechanism. The initial inward current was not eliminated by external application of high concentrations of tetrodotoxin, d-tubocurarine or amiloride. Nor was it affected by the intracellular application of cyclic GMP or cyclic AMP.

Infection and cancer: current state of art.

Empirical evidence of the association of cancer with parasitic and viral infectious agents has been recognized earlier. Today, viruses are thought to account for about 10% of all cancers and they take a central place in experimental cancer research. This area has expanded tremendously with modern molecular biology techniques, the knowledge of gene expression, cellular enzyme and mechanisms of transformation. However, the last proof of causality is not yet available. Serologic, virologic, experimental and protective evidence is needed to confirm the assumptions in this rapidly developing field of research. The prevention of hepato-cellular carcinoma by effective vaccines now available is, in the opinion of the WHO, at least theoretically possible.

Plague and Glasnost. First information about human cases in the USSR in 1989 and 1990.

In October 1989 the first case of plague death in the USSR was reported to WHO. This occurrence in man did not surprise plague experts. The country has extensive enzootic areas and the persistence of natural foci, which can be silent for many years, has been well studied. It is known that the plague bacillus can survive and multiply in the soil of rodent burrows and restart local or more extensive transmissions in carrier animals. Isolated cases in man can remain accidental or they may signal a larger epizootic outbreak. The official policy of the comprehensive antiplague services was to eradicate the natural foci by antirodent activities which proved impossible. The present report from the Central Asian part of the USSR in the wake of Glasnost augurs well for the surveillance of plague worldwide as for a period of over fifty years the occurrence of cases in man in this country had been denied.

[Attitude of medical students to alternative healing methods]. / Die Einstellung der Medizinstudenten zu alternativen Heilmethoden.

In Austria, the interest in alternative healing is obviously increasing, particularly among aspiring physicians. Several separate surveys were carried out by the Institute of Social Medicine in Graz among established physicians, general practitioner trainees and students of the Medical Faculty in order to learn something about their attitudes to alternative therapies. The surveys were directed towards the acceptance or refusal and the utilization of main alternative practices. The attempts show the difficulties in obtaining valid information. Only two satisfied the stringent criteria for the evaluation. This showed that popularity of alternative medicine was pronounced with students. The interest could be explained in part by the insufficiencies in the quality of medical education and by the influence of biased mass media.

[Alternative healing methods in Austria]. / Alternative Heilmethoden in Osterreich.

The term "alternative medicine" serves as collective name for all healing methods and medicines whose efficacy has not been confirmed by controlled studies and trials. The various methods are separated by a broad spectrum from the scientific opinions of official medicine. Some are close to conventional practice; they are tolerated or even partly integrated into the official healing system, which means that physicians are permitted to apply them. However, this tolerance of non-scientific methods has as consequence led to a weakening of the Austrian law. The official position with respect to the most widely used methods of alternative healing, as well as the aggressive trend towards a technology which supports alternative healing methods, are discussed.

[Succession from the viewpoint of the primary physician, education of the general physician. Results of a representative survey of faculty of Steiermark]. / Der Turnus aus der Sicht der Primarärzte, Ausbildung zum praktischen Arzt. Ergebnisse einer repräsentativen Befragung der Ausbildner in der Steiermark.

A study of post-graduate training for physicians, as viewed by the department-chiefs, was carried out in 1989 by the Institute of Social Medicine of the University in Graz, Austria, and compared with the opinions of the trainees themselves, as found in a previous study. The comparison shows that various differences exist, but also agreements between the answers of both studies. Both groups strongly emphasize the need to improve the curriculum of the post-graduate training and the quality control of the performance of trainees, as presently the training does not guarantee a uniform standard. The department-chiefs consider the university training as insufficient in up to 30% in theoretical, and 85% in practical fields.

Plague in Vienna.

The history of plague in one city--Vienna, Austria--has been traced from records beginning in the fourteenth century until its disappearance in the eighteenth century. Much of the source material for this review is published for the first time in English and is drawn from records maintained by the city of Vienna at the time of each outbreak. The historical context illustrates the reaction of large populations to deadly disease: fear, helplessness, and acceptance of an ever present threat. Concepts of prophylaxis to ward off the infection were haphazard, empiric, and often dependent on the use of medicaments and treatments that were, in modern terms, irrational. The medical and hygienic concepts of the time were principal impediments to more successful control, as is demonstrated by quotations from official documents dealing with attempts to cope with the epidemic. The development of control measures was painfully slow, and ultimate control was not achieved until socioeconomic improvement and concepts of hygiene both reached the point at which the conditions for the spread of the disease could be minimized.