Each time that you change the card details on your account a small temporary store holding charge may be applied to check that the card details are correct and valid and that it's registered to exactly the same name and address as on your iTunes account. They should disappear off your account within a few days or so - from http://support.apple.com/kb/HT3702
If you update your billing information, the iTunes Store or Mac App Store will place an authorization hold on your payment card account, usually in the amount of 1 USD or the local currency equivalent, to verify your account information.
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Authorization holds are removed by your financial institution shortly after your purchase clears. The time it takes to remove authorization requests varies by financial institution.
If they haven't disappeared then you could try contacting your card issuer, and you could also contact iTunes Support via the link that AnaMusic gave.