Biomedical subjects

W Hanke

Publications and source records attributed to W Hanke.

At least 181 records · Page 10Linked to original sources

PubMed1981

Agonist-activated ionic channels in acetylcholine receptor reconstituted into planar lipid bilayers.

Planar lipid bilayers were formed with the mixed chain phospholipid 1-stearoyl-3-myristolglycero-2-phosphocholine. Acetylcholine receptor membrane fragments or the purified receptor protein was incorporated into these bilayers by fusing receptor-containing vesicles with the planar membranes a few degrees below the lipid phase transition temperature. Single-channel currents activated by nicotinic agonists in the reconstituted system resembled those observed in intact rat and frog muscle membrane as measured by the patch clamp technique. The observed channel characteristics did not depend on the degree of receptor purification. Thus, the receptor-enriched fragments and those depleted of nonreceptor peripheral peptides, the purified receptor monomer/dimer mixtures, and the isolated receptor monomer as defined by gel electrophoresis all shared similar electrochemical properties in the synthetic lipid bilayer. The agonist-activated ionic channel seems, therefore, to be contained within the receptor monomer.

Acetylcholine↗

PubMed1980

The lowest conductance state of the alamethicin pore.

High resolution experiments of the alamethicin pore demonstrate the existence of a further pore state at low conductance values. This lowest resolved conductance state is found at 19 pS in 1 M KCl at room temperature. The value differs from that of the next higher conductance state by a factor of 14--15 and is approx. 20% lower than the gramicidin A pore conductance. The lowest conductance state seems to be impermeable to Ca2+, Cl-, Tris-H+ and Hepes-, whereas the higher conductance states are not.

Alamethicin↗

PubMed1980

Lipid phase transition in planar bilayer membrane and its effect on carrier- and pore-mediated ion transport.

Using mixed-chain lipids, we have recorded cooling and heating curves of planar bilayer membranes while they passed the lipid phase transition range. With unmodified planar bilayers, spontaneous current fluctuations are observed near the lipid phase transition temperature (tc approximately 29 degrees C). This effect coincides with the expected and measured decrease in membrane capacitance. Carrier (valinomycin)-modified planar bilayers exhibit near tc an abrupt change from a high-conducting state above tc to the state of bare membrane conductance below tc. In contrast to this behavior, planar bilayers modified by pore-forming antibiotics (gramicidin A, alamethicin) do not show any peculiar effect at tc. However, at 22--23 degrees C a pronounced maximum in pore-induced conductance is seen. Whereas the gramicidin A pore abruptly stops stepwise fluctuations below approximately 16 degrees C, with alamethicin a few long-lasting pore and pore state fluctuations persist down to 10 degrees C. It is suggested that the carrier may freeze out into the membrane/water interface. The effects observed with pore-forming substances, on the other hand, are interpreted in terms of lateral phase separation into pure lipid and lipid/antibiotic domains.

Alamethicin↗

PubMed1980