La troponina es un componente de los filamentos finos junto con la tropomiosina y es la proteína con la cual el calcio se une para ejecutar la regulación. La troponina tiene tres subunidades, TnC, TnI, y TnT. Cuando el calcio se une con los sitios específicos en la subunidad TnC, la tropomiosina se desplaza de los sitios activos en los filamentos finos, de modo que la miosina (un motor molecular organizado en los filamentos gruesos) puede unirse al filamento fino y producir fuerza o movimiento. En ausencia de calcio, la tropomiosina interfiere con la acción de la miosina y por ende el músculo se relaja. El músculo liso no tiene troponina.
Conclusiones
1. El calcio participa activamente en variados procesos celulares, entre ellos se destacan las vías de transducción de señales metabólicas, en las cuales constituye uno de los segundos mensajeros comprobados.
2. Las funciones demostradas de la vitamina D no se limitan al metabolismo del calcio, pues está comprobado que interviene en otros procesos tanto a nivel fisiológico como celular.
3. El sensor principal de calcio en el organismo es la glándula paratiroides, pero existen otros sensores de calcio específicos en los tejidos, como es el caso del sensor neuronal.
4. El calcio es efector alostérico o ligando de numerosas proteínas con variadas e importantes funciones, tanto a nivel celular como a nivel de organismo.
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