Bass amp for guitar---works fine
Guitar amp for bass---not recomended
The lower frequencies of bass will distort through a regular guitar amp, maybe you like that sound, (I do not.) Cranking the volume can also damage the speakers. Bass speakers are (generaly speaking) made of heavier/thicker materal and have wider voice coils and frequently larger magnets to allow them to handle the lower frequencies. Keyboard amps with extended bass work quite well for both guitar and bass as well as keyboards, this might be a better option to consider.