In Matt. 16:19 where the Lord Jesus Christ bestows the keys of the kingdom of Heaven upon the apostle Peter, the Greek text uses the plural declension of οὐρανός, as follows:
καὶ δώσω σοι τὰς κλεῖς τῆς βασιλείας τῶν οὐρανῶν καὶ ὃ ἐὰν δήσῃς ἐπὶ τῆς γῆς ἔσται δεδεμένον ἐν τοῖς οὐρανοῖς καὶ ὃ ἐὰν λύσῃς ἐπὶ τῆς γῆς ἔσται λελυμένον ἐν τοῖς οὐρανοῖς TR, 1550
However, in Matt. 18:18 where keys are bestowed upon the remainder of the apostles, the Greek text uses the singular declension of οὐρανός, as follows:
Ἀμὴν λέγω ὑμῖν ὅσα ἐὰν δήσητε ἐπὶ τῆς γῆς ἔσται δεδεμένα ἐν τῷ οὐρανῷ καὶ ὅσα ἐὰν λύσητε ἐπὶ τῆς γῆς ἔσται λελυμένα ἐν τῷ οὐρανῷ TR, 1550
What significance, if any, is there in the usage of the plural versus the singular declension of οὐρανός in two verses which seem to be referencing the same authority (i.e., binding and loosing) bestowed upon the apostles by the Lord Jesus Christ?