No, you can't assign a file to a single channel, per se, but you can do a work around. For the following to work, your image has to be in 24-bit RGB or CMYK color space.
With your image open, you can click on Image|Split Channels To| and then select a "format": RGB (red, green, blue), CMYK (cyan, magenta, yellow, black), HSB (hue, saturation, brightness), HLS (hue, lightness, saturation), YIQ (luminance and two chromacity values). This will create new greyscale images based upon which one of these you chose to split to... you could then work on each file individually and eventually merge them all back together (Image|Combine Channels).
One thing that I do now and then is to split the channels of a photo, copy one of the new files to the clipboard and then paste that image into my original working file and play with the merge modes in the Object Docker... you can improve some color casts this way, improve contrast, etc. Lots of stuff to play with there.
You can also split to LAB (luminosity and two hue channels), but your image has to be in the LAB colorspace to begin with.
These split channels show the entire image. You can also work with some channels directly via the Channel docker but it will only show you the channels that are available in your current colorspace.
You may want to look at the Image|Calculations area for working on Channels, too (I don't know much about working with calcs, just know it's there

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