PubMed · 4585684
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K Murakami, T Inagami, A M Michelakis, S Cohen. 1973-09-18. An affinity column for renin.. https://doi.org/10.1016/0006-291x(73)91446-0
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Four types of ion-selective channels were found by the patch-clamp technique in the human erythroleukemia K562 cells. I) in cell-attached configuration at potentials less negative than -40 mV an 8 ps channel was detected. The potential dependence of channel activity suggests that this is the TTX-sensitive Na+ channel. II) A cation-selective channel was observed with equal permeability for Na+ and K+ and a potential-independent single-channel conductance of 19 pS. The channel is activated by intracellular Ca2+ and inhibited by TEA, III) A predominantly anion-selective channel was identified with the selectivity sequence NO3- > J- > Cl- = Br- >> SO4(2-). The single-channel conductance shows outward rectification, and is in symmetrical NaCl solution 19 pS at -60 mV and 54pS at +50 mV. The open- and closed-time distributions suggest one open and at least four closed states. At submicromolar concentrations, the open state is blocked by H2DIDS leading to channel flicker between open and blocked channel; higher concentrations (apparent KI = 6.8 uM) lead to a longer-lasting blocked state. Both components of inhibition are reversible. IV) In addition, an 8 pS, Na(+)- and K(+)- selective channel could be induced by application of palytoxin. For channel activity, the presence of extracellular Na+ is essential. It is assumed that the Na+, K(+)-pump molecule is involved in the channel formation. Similarly, it is discussed whether the anion-selective channel represents a pore conformation of an electrically silent anion exchanger.
Palytoxin (PTX) induces a cation channel through interaction with Na(+),K(+)-ATPase. It is unclear how this action relates to the enzyme catalytic activity. We examined whether the action of PTX depends on the catalytic domain specific for Na(+),K(+)-ATPase. Wild-type Na(+),K(+)-ATPase alpha-subunit (NNN) or its chimera (NCN), in which the catalytic domain was replaced with that of sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase, was co-expressed with beta-subunit in the yeast Saccharomyces cerevisiae. PTX (0.1-100 nM) increased K(+) efflux in NNN- or NCN-transfected cells to a similar degree but not in non-transfected cells. When ouabain-resistant NNN and NCN were expressed, PTX also increased K(+) efflux. Ouabain inhibited the effect of PTX in NNN or NCN cells but not in ouabain-resistant cells. These data suggest that the channel-forming action of PTX does not depend on the catalytic domain species.
The volume phase transition behavior of a poly(N-isopropylacrylamide) gel (NIPA gel) in solutions of N-acyl amino acid surfactants were studied as a function of surfactant concentration. The addition of a surfactant beyond the critical micelle concentration (cmc) produced elevation in the transition temperature of the NIPA gel and its swelling. The changes in the volume phase transition temperature and in the swelling of the NIPA gel became more significant with the decreasing size of the amino acid side chain. This result could almost be explained only by the binding amount of surfactant onto the NIPA gel regardless of molecular structure of the amino acid. The binding amount increased in the order of sodium N-lauroyl-glycinate>-alaninate>-valinate>-leucinate>or=-phenylalaninate. For an N-acyl amino acid surfactant to bind onto the NIPA gel, to increase the transition temperature, and to facilitate swelling of the gel, the steric hindrance of the amino acid side chain was more effective than its hydrophobicity.