Acute temperature sensitivity in optic nerve axons explained by an electrogenic membrane potential.

Classical work in squid axon reports resting membrane potential is independent of temperature, but our findings suggest that this is not the case for axons in mammalian optic nerve. Refractory period duration changes over 10 times between 37 °C and room temperature, and afterpotential polarity is also acutely temperature sensitive, inconsistent with changes in temperature impacting nerve function only through altered rates of ion channel gating kinetics. Our evidence suggests that the membrane potential is enhanced by warming, an effect reduced by exposure to ouabain. The temperature dependence can be explained if axonal Na(+)/K(+) ATPase continuously expels Na(+) ions that enter axons largely electroneutrally, thereby adding a substantial electrogenic component to the membrane potential. Block of the Na(+) transporter NKCC1 with bumetanide increases refractoriness, like depolarization, indicating that this is a probable route by which Na(+) enters, raising the expectation that the rate of electroneutral Na(+) influx increases with temperature and suggesting a temperature-dependent transmembrane Na(+) cycle that contributes to membrane potential.

"You must do the test to know your status": attitudes to HIV voluntary counseling and testing for adolescents among South African youth and parents.

Reduced HIV risk behavior and increased use of care and support services have been demonstrated among adults accessing HIV voluntary counseling and testing (VCT). The impact of VCT on adolescents is, however, not known. Focus group discussions were held with adolescents and parents in two South African townships to establish the perceptions of and needs for VCT among young people. Ecological theory informed the analysis. Adolescents had limited experience of VCT, were afraid of knowing their HIV status, and felt that testing was only for symptomatic individuals. Youth felt that they would disclose their HIV status to family members who they felt would be most supportive. Youth were afraid of stigma and discrimination; rarely referring to the community as a source of support. Discussions highlighted the inappropriateness of clinical facilities for youth VCT. We conclude with recommendations for youth-friendly VCT services.