PR and adsense earning are 2 different things. An increase or decrease in PR shouldn't affect your earnings. SticKer
PR has no relationship with CTR or another thing related to adsense. PR is basically a scale showing the amount of backlinks[link popularity] a site have.
No. They are independent of each other Pr depends on backlinks ecpm depends on your content, keyword density etc CPM depends on how well you have blended the ads with content and what is the extent of ads matching your content