There are a lot of different ways of utilising leverage. They do not necessarily involve the use of credit.
Puts and calls are terms used in traded options which was what I described. Options can be traded as separate entities. Have a look at the liffe market for stock options.
 If I open an account at a stockbrokers, a forex account or a spread betting account I can use leverage but it is unlikely that I will be extended credit and I will only be allowed to lose what I have in my account at which point any open position will be automatically closed.
 
 There is often confusion about whether money is actually being loaned in a futures contract. Elsewhere in this forum you can read statements such as
"Alternatively, you could open a $1000 long position in the BTC/USD pair on margin. This is an open trading position only and no profit/loss is realized until it is closed. There is no currency conversion and you don't own any BTC that you can withdraw"
 But later they say
"To give a rough idea, the margin fee will work something like this. Suppose you open a $1000 long position in BTC/USD using margin. In doing so, you are borrowing the $1000 from us and we will charge an APR for this, but the fees will be assessed at least on a daily basis"
 So I'm borrowing the money and being charged interest but can't withdraw it. The exchange wins every time.

 If the blockchain did contain information on other currency transactions then it might be possible to operate a derivatives market. Imagine if the Litecoin and bitcoin blockchains were combined and the proof of work was applied to both combined blockchains. We could then build an exchange and a derivatives market between litecoin and bitcoin. If fiat currencies became available in digital format we could just have one big blockchain for all financial transactions in whatever currency.