Credit Card debt is a part of the money supply. But the Fed doesn’t count it as such for some reason.

“When someone uses a credit card in a purchase, he automatically expands the money supply. The seller receives a new deposit in his account, which increases the total of demand deposits in the banking system — until the buyer pays off the loan. The result is that consumers who roll over their credit card loans rather than paying them off have increased the money supply on their own initiative by hundreds of billions of dollars. In effect, the money supply is substantially larger and less measurable than the Fed’s definition.”
http://wfhummel.cnchost.com/moneysupply.html

In theory, lower interest rates make borrowing cheaper. Which encourages more borrowing and thus expands the money supply through Fractional Reserve Banking. But this works only when banks have the money to lend and consumers are able and willing to borrow.

Which is why the present low interest rates are not having the desired effect of expanding the money supply. Many banks are hiding bad loans on their books. And they are not in a good shape to lend more. And many consumers already have too much debt and are either unwilling or unable to borrow more.