1. Cyclical pressurization of cultured chondrocytes results in increases in cyclic AMP and in the rate of proteoglycan synthesis. Intermittent increases in hydrostatic pressure are also associated with hyperpolarization of chondrocyte cell membranes and activation of Ca(2+)-dependent K(+)-ion channels but the physiological basis for this response to mechanical stimulation is unclear. 2. Experiments have been undertaken to better define the types of ion channels involved and to explore the possibility that the hyperpolarization response associated with cyclical pressurization of chondrocytes follows activation of stretch-activated ion channels. 3. The mean membrane potential of chondrocytes in non-confluent monolayer cell culture rose from -15.3 +/- 0.24 mV to -21.1 +/- 0.28 mV (n = 60, P< 0.0001) after intermittent pressurization (0.33 Hz, 16 kPa, 20 min). 4. Strain gauge measurements showed that cyclical pressurization was associated with strain on the base of the culture plate. The amplitude of the hyperpolarization response was proportional to the microstrain to which cells were subjected. 5. Membrane hyperpolarization did not occur when chondrocytes were subjected to cyclical pressurization in rigid glass culture dishes or plastic dishes positioned in the pressurization chamber so as to avoid bending of the base of the culture dish. 6. Indirect evidence that the hyperpolarization response after intermittent pressure-induced strain was associated with stimulation of stretch-activated ion channels was obtained from experiments with gadolinium, amiloride and hexamethylene amiloride, each of which abolished hyperpolarization. 7. Experiments with apamin, charybdotoxin and iberiotoxin showed that the Ca(2+)-activated K+ channels involved in the hyperpolarization response are apamin-sensitive, charybdotoxin- and iberiotoxin-resistant, low-conductance channels. 8. Somatostatin and cadmium chloride, which block L-type calcium channels, abolished strain-induced chondrocyte hyperpolarization. EGTA, which chelates extracellular Ca2+, reduced the response to 48% of control values, and thapsigargin, which raises intracellular Ca2+ by inhibition of Ca(2+)-ATPase in endoplasmic reticulum, caused hyperpolarization independently with further hyperpolarization after pressure-induced strain. These data indicate that chondrocyte hyperpolarization was dependent on intracellular Ca2+ concentrations. 9. Further work is required to determine whether stretch-activated ion channels shown to be associated with chondrocyte hyperpolarization after cyclical pressure-induced strain are also involved in the signal transduction process that leads to increases in proteoglycan synthesis.

Mechanical stimuli influence chondrocyte metabolism, inducing changes in intracellular cyclic adenosine monophosphate and proteoglycan production. We have previously demonstrated that primary monolayer cultures of human chondrocytes have an electrophysiological response after intermittent pressure-induced strain characterised by a membrane hyperpolarisation of approximately 40%. The mechanisms responsible for these changes are not fully understood but potentially involve signalling molecules such as integrins that link extracellular matrix with cytoplasmic components. The results reported in this paper demonstrate that the transduction pathways involved in the hyperpolarisation response of human articular chondrocytes in vitro after cyclical pressure-induced strain involve alpha 5 beta 1 integrin. We have demonstrated, using pharmacological inhibitors of a variety of intracellular signalling pathways, that the actin cytoskeleton, the phospholipase C calmodulin pathway, and both tyrosine protein kinase and protein kinase C activities are important in the transduction of the electrophysiological response. These results suggest that alpha 5 beta 1 is an important chondrocyte mechanoreceptor and a potential regulator of chondrocyte function.

Adhesion and colonization are prerequisites for the establishment of bacterial pathogenesis. The prevention of adhesion is an attractive target for the development of new therapies in the prevention of infection. Bacteria have developed a multiplicity of adhesion mechanisms commonly targeting surface carbohydrate structures, but our ability to rationally design effective antiadhesives is critically affected by the limitations of our knowledge of the human ‘glycome’ and of the bacterial function in relation to it. The potential for the future development of carbohydrate-based antiadhesives has been demonstrated by a significant number of in vitro and in vivo studies. Such therapies will be particularly relevant for infections of mucosal surfaces where topical application or delivery is possible.

Background: An acidic polysaccharide, fCS, from the sea cucumber Holothuria forskali has a range of biological activities.Results: The conformation of fCS was determined, and resulting oligosaccharides were shown to retain desirable biological properties.Conclusion: The conformation of the fCS repeating unit underpins binding to L- and P-selectins.Significance: Exploitation of the fCS-selectin interaction may open new avenues for therapeutic intervention using fCS fragments or their mimetics.