The interaction of the peptide antibiotic nisin with liposomes has been studied. The effect of this interaction was analyzed on the membrane potential (inside negative) and the pH gradient (inside alkaline) in liposomes made from Escherichia coli phosphatidylethanolamine and egg phosphatidylcholine (9:1, wt/wt). The membrane potential and pH gradient were generated by artificial ion gradients or by the oxidation of ascorbate, N, N,N',N'-tetramethyl-p-phenylenediamine, and cytochrome c by the beef heart cytochrome c oxidase incorporated in the liposomal membranes. Nisin dissipated the membrane potential and the pH gradient in both types of liposomes and inhibited oxygen consumption by cytochrome c oxidase in proteoliposomes. The dissipation of the proton motive force in proteoliposomes was only to a minor extent due to a decrease of the oxidase activity by nisin. The results in these model systems show that a membrane potential and/or a pH gradient across the membrane enhances the activity of nisin. Nisin incorporates into the membrane and makes the membrane permeable for ions. As a result, both the membrane potential and pH gradient are dissipated. The activity of nisin was found to be influenced by the phospholipid composition of the liposomal membrane.

Gap junction channels are structurally distinct from other ion channels in that they comprise two hemichannels which interact head-to-head to form an aqueous channel between cells. Intercellular voltage differences together with increased intracellular concentrations of H+ and Ca2+ cause closure of these normally patent channels. The relative sensitivity to voltage varies with the subunit (connexin) composition of the channels. The third of four transmembrane-spanning regions (M3) in connexins has been proposed to form the channel lining, and a global 'tilting' of the hemichannel subunits has been correlated with channel closure. But specific components involved in transduction of channel gating events have not been identified in either gap junctions or other ion channel classes (however, see model in ref. 5). We have examined a strictly conserved proline centrally located in M2 of connexin proteins. Mutation of this proline (Pro 87) in connexin 26 causes a reversal in the voltage-gating response when the mutant hemichannel is paired with wild-type connexin 26 in the Xenopus oocyte system. This suggests that the unique properties associated with this residue are critical to the transduction of voltage gating in these channels.

Tonometry is a fundamental procedure in routine ophthalmologic examination. Although regarded as the reference standard, the Goldmann applanation tonometer (GAT) has its limitations. A new portable alternative to the GAT is the iCare rebound tonometer (RT). The aim of the present study was to compare the intraocular pressure (IOP) results obtained using the RT and GAT and then correlate the results with the central corneal thickness (CCT). Moreover, the tolerability and safety of the RT were evaluated. The IOP of 336 patients (672 eyes) was determined by the RT and GAT. The patients were divided into three groups (group A, 7–15 mmHg, n=74; group B, 16–22 mmHg, n=218; and group C, 23–50 mmHg, n=44), based on the GAT IOP readings. Pachymetry and slit lamp inspection were also performed. To establish an agreement between the devices, a Bland-Altman analysis and paired t-test were performed. The correlation between CCT and IOP readings obtained by the two devices were assessed using linear regression correlation analysis. The mean IOP values of the RT and the GAT were 18.30±5.10 and 18.52±4.46 mmHg, respectively. There were no significant differences between them (t=−1.31, P=0.19). The 95% confidence interval of the differences between the two devices was −5.80–6.24 mmHg. The RT readings are correlated well with those of GAT (r=0.806, P=0.001). However, the RT measurements were significantly (t=−2.84, P=0.007) lower (−1.66±3.87 mmHg) than those obtained with GAT when GAT ≥23 mmHg. Both the RT (r=0.390, P=0.001) and the GAT (r=0.191, P=0.001) showed positive correlations with CCT. The IOP measurement with RT was well tolerated. None of the corneal epithelial defects was detected and all subjects denied discomfort. The RT is well tolerated and safe, and can be considered a reliable alternative to GAT for patients in a low to moderate IOP range. However, in patients with high IOP values, the measurements obtained with RT did not correlate well with those obtained by GAT. The RT readings are influenced more by CCT compared to GAT.

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