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When a hair cell is stimulated by positive deflection of its hair bundle, increased tension in gating springs opens transduction channels, permitting cations to enter stereocilia and depolarize the cell. [Ca.sup.2+] is thought to be required in mechanoelectrical transduction, for exposure of hair bundles to [Ca.sup.2+] chelators eliminates responsiveness by disrupting tip links, filamentous interstereociliary connections that probably are the gating springs. [Ca.sup.2+] also participates in adaptation to stimuli by controlling the activity of a molecular motor that sets gating-spring tension. Using a flexible glass fiber to measure hair-bundle stiffness, we investigated the effect of [Ca.sup.2+] concentration on stiffness before and after the disruption of gating springs. The stiffness of intact hair bundles depended nonmonotonically on the extracellular [Ca.sup.2+] concentration; the maximal stiffness of [approximately equal to] 1200 [Mu]N[center dot][m.sup.-1] occurred when bundles were bathed in solutions containing 250 [[micro]molar] [Ca.sup.2+], approximately the concentration found in frog endolymph. For cells exposed to solutions with sufficient chelator capacity to reduce the [Ca.sup.2+] concentration below [approximately equal to] 100 nM, hair-bundle stiffness fell to [approximately equal to] 200 [Mu]N[center dot][m.sup.-1] and no longer exhibited [Ca.sup.2+]-dependent changes. Because cells so treated lost mechanoelectrical transduction, we attribute the reduction in bundle stiffness to tip-link disruption. The results indicate that gating springs are not linearly elastic; instead, they stiffen with increased strain, which rises with adaptation-motor activity at the physiological extracellular [Ca.sup.2+] concentration.

The mechanoelectrical-transduction channel of the hair cell is permeable to both monovalent and divalent cations. Because [Ca.sup.2+] entering through the transduction channel serves as a feedback signal in the adaptation process that sets the channel's open probability, an understanding of adaptation requires estimation of the magnitude of [Ca.sup.2+] influx. To determine the [Ca.sup.2+] current through the transduction channel, we measured extracellular receptor currents with transepithelial voltage-clamp recordings while the apical surface of a saccular macula was bathed with solutions containing various concentrations of [K.sup.+], [Na.sup.+], or [Ca.sup.2+]. For modest concentrations of a single permeant cation, [Ca.sup.2+] carried much more receptor current than did either [K.sup.+] or [Na.sup.+]. For higher cation concentrations, however, the flux of [Na.sup.+] or [K.sup.+] through the transduction channel exceeded that of [Ca.sup.2+]. For mixtures of [Ca.sup.2+] and monovalent cations, the receptor current displayed an anomalous mole-fraction effect, which indicates that ions interact while traversing the channel's pore. These results demonstrate not only that the hair cell's transduction channel is selective for [Ca.sup.2+] over monovalent cations but also that [Ca.sup.2+] carries substantial current even at low [Ca.sup.2+] concentrations. At physiological cation concentrations, [Ca.sup.2+] flux through transduction channels can change the local [Ca.sup.2+] concentration in stereocilia in a range relevant for the control of adaptation.

Electron microscopic and differential scanning calorimetric studies of the sporicidal action of H2O2 reveal that H2O2 killing of bacterial spores increases with acidification and temperature rise. Transition metal cations such as Cu2+, Co2+, Fe3+ and Mn2+ and metal chelators offer varied protection to spores from killing by H2O2. Radical scavengers and antioxidants such as L-histidine and superoxide dismutase offer the least protection against H2O2 sporicidal action. H2O2 reacts with spores through formation of reactive hydroxyl radicals by catalysts.

The acid tolerances and inhibitor sensitivities of F-ATPases, isolated by detergent extraction, from three oral lactic acid bacteria, Lactobacillus casei ATCC 4646, Streptococcus mutans GS-5 and Streptococcus sanguis NCTC 10904, were compared. The pH optima for activity of the membrane-associated enzymes reflected the overall acid tolerances of the organisms. Fluoroaluminate complexes were inhibitory for isolated F(sub 1)F(sub 0) and F(sub 1) enzymes.