| Título: | Developmental regulation of calcium-dependent feedback in Xenopus rods |
| Autores: |
Solessio, Eduardo Mani, Shobana S. Cuenca Navarro, Nicolás Engbretson, Gustav A. Barlow, Robert B. Knox, Barry E. |
| Fecha: |
2008-10-08 2008-10-08 2004-10-25 |
| Publicador: | RUA Docencia |
| Fuente: |
 |
| Tipo: | info:eu-repo/semantics/article |
| Tema: |
Signal transduction Photoreceptors G protein cascade Retina Adaptation Fisiología |
| Descripción: |
The kinetics of activation and inactivation in the phototransduction pathway of developing
Xenopus
rods were studied. The gain of the activation steps in transduction (amplification) increased and photoresponses
became more rapid as the rods matured from the larval to the adult stage. The time to peak was significantly
shorter in adults (1.3 s) than tadpoles (2 s). Moreover, adult rods recovered twice as fast from saturating flashes
than did larval rods without changes of the dominant time constant (2.5 s). Guanylate cyclase (GC) activity,
determined using IBMX steps, increased in adult rods from
~1.1 s–1 to 3.7 s–1 5 s after a saturating flash delivering
6,000 photoisomerizations. In larval rods, it increased from 1.8 s–1 to 4.0 s–1 9 s after an equivalent flash. However,
the ratio of amplification to the measured dark phosphodiesterase activity was constant. Guanylate cyclase–activating
protein (GCAP1) levels and normalized Na+/Ca2+, K+ exchanger currents were increased in adults compared
with tadpoles. Together, these results are consistent with the acceleration of the recovery phase in adult rods via
developmental regulation of calcium homeostasis. Despite these large changes, the single photon response
amplitude was ~0.6 pA throughout development. Reduction of calcium feedback with BAPTA increased adult
single photon response amplitudes threefold and reduced its cutoff frequency to that observed with tadpole
rods. Linear mathematical modeling suggests that calcium-dependent feedback can account for the observed
differences in the power spectra of larval and adult rods. We conclude that larval
Xenopus
maximize sensitivity at
the expense of slower response kinetics while adults maximize response kinetics at the expense of sensitivity. This work was supported by the National Institutes of Health grants EY-11256 and EY-12975 (B.E. Knox), EY-00667 (R.B. Barlow), and EY-13772 (G.A. Engbretson), Research to Prevent Blindness (unrestricted grant to SUNY UMU Department of Ophthalmology and Career Development Awards to E. Solessio and S.S. Mani) and Lions of CNY. |
| Idioma: | Inglés |
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