- Email: [email protected]
S-G1-02 Phototransduction in Drosophila
Symposia Lectures s-G1-01 RECEPTORS AND TRANSDUCTION PATHWAYS IN OLFACI’ORY NEURONS BREER, H. Institute of Zoophysiology, Univ. StuttgartHohenheim (Germany)
S-F3-03 RANDOM WALKING DURING QUIET STANDING COLLINS JJ. Dept. of Biomedical Eng.. Boston University (USA) Purpose: During quiet standing, the human body continually moves about in an ermtic., and ssibly chaotic, fashion. Our objective in th~s stu 8”y was to determine whether balance regulation is better represented as a chaotic process or a stochastic process.
Odorants are detected by chemosensory neurons which encode the strength, duration and quality of odorous stimuli mto afliient neuronal wgnals. Upon interaction of odorous molecules with s ciiic receptors in the chemosensorymemr rane of olfactory neurons, second messengerpathways are activated via G-proteins leadmg to a rapid and transient rise in the concentrationof either CAMP or IP3. The secondmessenger‘pulses’are supposedto elicit generator currents via direct g&g of cation channels. The rapid termination of odorinduced second messen er signalling is accom lished by uncoup7.mg the reaction cascaBe via a ne tive feedback reaction leadin to ret tor p osphorylation Em loyin recom%inantl!&A bz!mques new ~e&ers d a gene family encodin butative odorant receptors have been I*dentified. Receptorencoding cDNAs have been expressedin Sf9cells which generated second messenger responses upon stimulation with appropriate odorants.
Methods: Ten heaithy young subjects were studied under quiet-standing conditions. Postural sway was quantified by measuring the time-varyink cbsplacements of the center of pressure under each subJect’s feet. Techniques from dynamical systems theory (e.g., Lyapunov exponent computation and surrogate data techniques) and random walk theory were applied to the postural sway data. Results: We found that human postural sway is indistinguishable from conelated noise and that it can best be mode&d as a system of bounded, correlated random walks. More specifically, we found the presence of short-range positivecorrelations andlongrange negative correlations in postural sway data. Conclusions: These novel results suggest that the human postural control system utilizes open-loop and closed-loop control mechanisms over short-term and long-term time intervals, nxpectively. The integration of open-loop control schemes with closed-loop feedback mechanisms for balanceregulationmayhaveevolved to account for feedback-loot, delays and inherent noise in the system, and to simpl8y the-task of integrating vast amounts of sensory information when the body is not in jeopardy of instability.
S-Gl-03 HAIR CELL M?XHANO-TRANSDUCTION van NETTEN, SM.
S-Gl-02 PHOTOTRAN$WCTION HARDIE RC. Department of University,
Cambridge
IN DIPOSOP~ILA Anatomy,
Ca&idge
Department
(UK)
of Biophysics,
University
of Groningen,
(NL)
Hair cells are the primary mechanoreceptorsof vertebratesand,are used to extract mechanicat signalsfrom their environment. Thesecells havea mechanosensitivebundle, usually consisting of severaltens of stiff stmovilli. Deflections of the stereovilli as small as fractions of a nanometer open the transduction channelsand result in changesof the membrane potential. The first stage of the tranaducMn pmcessis still poorly understood. One hypothesis,‘basedon in vitro observationsof reduced liair bundle stiffness in
Purpose: The light responsein Drosophila photoreceptors involves an influx of Ca*‘, mediated by the phosphoinooitide (PI) cascade. In many other cells, PI-mediated Ca* influx is activated by depletion of Ca* stores.Does such so-called “capacitative Ca*’ entry” underlie phototransduction in Drosophila? Methods: SimuItane~usCa*’ measurementsand whole-cell recordings were ,+dt from dissociatedDrosophila photoreceptors in Ca” free Ringer’s solution. Results: Saturating light stimuli failed to release detectable levelsof Ca2* from intracellular stores.By contrast, ioMMlycin r&a& C!a*’ in a saturating manner, but under nontlpi oondiions failed to activate any comjuctance.However, when the phot0recept0rswere loaded with CaBAPTA mixtures buffering Ca” at Z 10nM, ionomycin consistently activated the lightsensitive conductance. Conclusions: The hypothesis that phototransduction in Drosophila may be mediated by a proceaaanalogousto capacitative Ca*’ entry will be critically discussed.
response
lo hair
bundle
deflection,
is that the
transductionchannelsare directly engaged by elastic meehan+callinkages (gating springs). We studied the mechanicsof the late&l line cupula and the hair cells attached to it wiqg laser interferow. It was found that the stiffness of the hair lnmdles almost compktely determinesthe mechanicalpropertiesof the cupola and therefore controls the frequency selectivity of this organ. Becauseof this property, we are able to study the mechanicalchangesof the &an&u&on channels under the influence of pharmacological manipulations and test fiuther hypotheseson the meclisni~.d#ile #e&g of the tra0sduction channelsunder in vivo conrlitians. 18
S-F3-03 RANDOM WALKING DURING QUIET STANDING COLLINS JJ. Dept. of Biomedical Eng.. Boston University (USA) Purpose: During quiet standing, the human body continually moves about in an ermtic., and ssibly chaotic, fashion. Our objective in th~s stu 8”y was to determine whether balance regulation is better represented as a chaotic process or a stochastic process.
Odorants are detected by chemosensory neurons which encode the strength, duration and quality of odorous stimuli mto afliient neuronal wgnals. Upon interaction of odorous molecules with s ciiic receptors in the chemosensorymemr rane of olfactory neurons, second messengerpathways are activated via G-proteins leadmg to a rapid and transient rise in the concentrationof either CAMP or IP3. The secondmessenger‘pulses’are supposedto elicit generator currents via direct g&g of cation channels. The rapid termination of odorinduced second messen er signalling is accom lished by uncoup7.mg the reaction cascaBe via a ne tive feedback reaction leadin to ret tor p osphorylation Em loyin recom%inantl!&A bz!mques new ~e&ers d a gene family encodin butative odorant receptors have been I*dentified. Receptorencoding cDNAs have been expressedin Sf9cells which generated second messenger responses upon stimulation with appropriate odorants.
Methods: Ten heaithy young subjects were studied under quiet-standing conditions. Postural sway was quantified by measuring the time-varyink cbsplacements of the center of pressure under each subJect’s feet. Techniques from dynamical systems theory (e.g., Lyapunov exponent computation and surrogate data techniques) and random walk theory were applied to the postural sway data. Results: We found that human postural sway is indistinguishable from conelated noise and that it can best be mode&d as a system of bounded, correlated random walks. More specifically, we found the presence of short-range positivecorrelations andlongrange negative correlations in postural sway data. Conclusions: These novel results suggest that the human postural control system utilizes open-loop and closed-loop control mechanisms over short-term and long-term time intervals, nxpectively. The integration of open-loop control schemes with closed-loop feedback mechanisms for balanceregulationmayhaveevolved to account for feedback-loot, delays and inherent noise in the system, and to simpl8y the-task of integrating vast amounts of sensory information when the body is not in jeopardy of instability.
S-Gl-03 HAIR CELL M?XHANO-TRANSDUCTION van NETTEN, SM.
S-Gl-02 PHOTOTRAN$WCTION HARDIE RC. Department of University,
Cambridge
IN DIPOSOP~ILA Anatomy,
Ca&idge
Department
(UK)
of Biophysics,
University
of Groningen,
(NL)
Hair cells are the primary mechanoreceptorsof vertebratesand,are used to extract mechanicat signalsfrom their environment. Thesecells havea mechanosensitivebundle, usually consisting of severaltens of stiff stmovilli. Deflections of the stereovilli as small as fractions of a nanometer open the transduction channelsand result in changesof the membrane potential. The first stage of the tranaducMn pmcessis still poorly understood. One hypothesis,‘basedon in vitro observationsof reduced liair bundle stiffness in
Purpose: The light responsein Drosophila photoreceptors involves an influx of Ca*‘, mediated by the phosphoinooitide (PI) cascade. In many other cells, PI-mediated Ca* influx is activated by depletion of Ca* stores.Does such so-called “capacitative Ca*’ entry” underlie phototransduction in Drosophila? Methods: SimuItane~usCa*’ measurementsand whole-cell recordings were ,+dt from dissociatedDrosophila photoreceptors in Ca” free Ringer’s solution. Results: Saturating light stimuli failed to release detectable levelsof Ca2* from intracellular stores.By contrast, ioMMlycin r&a& C!a*’ in a saturating manner, but under nontlpi oondiions failed to activate any comjuctance.However, when the phot0recept0rswere loaded with CaBAPTA mixtures buffering Ca” at Z 10nM, ionomycin consistently activated the lightsensitive conductance. Conclusions: The hypothesis that phototransduction in Drosophila may be mediated by a proceaaanalogousto capacitative Ca*’ entry will be critically discussed.
response
lo hair
bundle
deflection,
is that the
transductionchannelsare directly engaged by elastic meehan+callinkages (gating springs). We studied the mechanicsof the late&l line cupula and the hair cells attached to it wiqg laser interferow. It was found that the stiffness of the hair lnmdles almost compktely determinesthe mechanicalpropertiesof the cupola and therefore controls the frequency selectivity of this organ. Becauseof this property, we are able to study the mechanicalchangesof the &an&u&on channels under the influence of pharmacological manipulations and test fiuther hypotheseson the meclisni~.d#ile #e&g of the tra0sduction channelsunder in vivo conrlitians. 18