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Control de retroalimentación altamente cooperativo de la guanilato ciclasa del bastón retiniano por iones de calcio
1Department of Cell Biology, Stanford University School of Medicine, California 94305.
Nature
|July 7, 1988
Resumen
La reducción de los niveles de calcio en las células varillas de la retina aumenta significativamente la actividad de la guanilato ciclasa, crucial para restaurar la visión después de la exposición a la luz. Este hallazgo pone de relieve el calcio.
Área de la Ciencia:
- La bioquímica es la bioquímica.
- Biología celular Biología celular.
- La neurociencia es la neurociencia.
Sus antecedentes:
- La excitación visual en las células varillas de la retina implica una cascada que reduce la GMP cíclica (cGMP) y cierra los canales.
- La recuperación del estado oscuro requiere la resíntesis de cGMP, catalizada por la guanylato ciclasa.
- Se hipotetiza que la reducción del calcio citosólico (Cai) después de la iluminación estimula la actividad de la guanilato ciclasa.
Objetivo del estudio:
- Para investigar el efecto de los niveles de calcio en la actividad de la guanylato ciclasa en los segmentos externos de las varillas.
- Para dilucidar el mecanismo de la regulación de la guanylata ciclasa por el calcio en la recuperación visual.
Principales métodos:
- Medición de la actividad de la guanilato ciclasa en los segmentos externos de las varillas bovinas a diferentes concentraciones de calcio.
- Investigando el papel de una proteína soluble en la activación de la guanilato ciclasa dependiente del calcio.
- Utilizando lavados de amortiguador bajos en sal para liberar y volver a agregar proteínas asociadas a la membrana.
Principales resultados:
- La actividad de la guanilato ciclasa en los segmentos externos no iluminados de las varillas bovinas aumentó entre 5 y 20 veces cuando el calcio se redujo de 200 nM a 50 nM.
- Esta dependencia del calcio mostró una fuerte respuesta cooperativa con un coeficiente de Hill de 3.9.
- Una proteína soluble liberada por el amortiguador de baja sal mediaba la sensibilidad al calcio, parcialmente restaurada por su re-adición.
Conclusiones:
- La actividad de la guanilato ciclasa es altamente sensible a los niveles fisiológicos de calcio en los segmentos externos de las varillas.
- Un factor proteico media la activación cooperativa de la guanylato ciclasa por la reducción de calcio inducida por la luz.
- Esta regulación dependiente de la luz de la guanylata ciclasa por el calcio es fundamental para restaurar la corriente oscura después de la excitación visual.
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