Google Refusing Email due to PTR Record

Google GMail is refusing my email, evidently because while my domain resolves to the correct static IP address, Comcast DNS servers are still resolving the PTR requests to the default standard comcast DNS name.

Who do I contact about getting that record removed from Comcast's DNS servers?

Yes, I already have another registrar whose name servers are serving my domain . . . I just hadn't bothered with the PTR record 'cause up 'til now, nobody seemed to use it for "security purposes."

Thanks,

John S.