What reason does Antonio give both for Salarino and Salanio to depart?

In act 1, scene 1, Antonio's feeling down in the dumps but doesn't know why. His friends Solanio and Salarino try to get to the bottom of the matter. They offer some suggestions as to why Antonio's feeling so blue. Perhaps he has business worries? After all, a number of his merchant ships laden with valuable cargo have just set sail upon the high seas. Salarino says that he'd be constantly worried if he were in Antonio's shoes. All it would take is for one single storm to destroy his ships and all their precious cargo.
But that's not the reason why Antonio's feeling miserable. Nor, for that matter, is it because he's in love, as Solanio suggests. Antonio's friends are trying their best to cheer up their old pal, but there's not much they can do to lift the gloom. They think it best if they leave Antonio to his "worthier friends"—Bassanio, Lorenzo, and Gratiano. In any case, Antonio doesn't want Solanio and Salarino to waste their precious time on him. They must have important business to attend to, and so he bids them farewell:

I take it your own business calls on you And you embrace th' occasion to depart.