Comparison between the properties of BCDs (squares) and of dIrrs (dots). The dIrrs are taken from Swaters et al. (2009), selecting the objects with high-quality rotation curves and V_rot < 70 km s^-1 at the last measured point. The BCDs are UGC 4483 (this work), I Zw 18 (Lelli et al. 2012), NGC 6789 (Lelli et al., in prep.), and NGC 1705 (Meurer et al. 1998). Some galaxies are labelled according to their UGC number. Left: R-band central surface brightness (inclination corrected) versus the inner rotation-velocity gradient V_rot(R₀)/R₀, where R₀ is the optical scale-length. Right: peak H I surface density Σ_{H   I,   peak} versus V_rot(R₀)/R₀. Σ_{H   I,   peak} is derived from the azimuthally-averaged H I surface density profiles. See Sect. 4 for details.