Shares in Fremont General Corp. surged as high as 22 percent during heavy trading Friday after the lender said Thursday that Credit Suisse AG increased the struggling mortgage lender’s line of credit to $1 billion.

The loan adds to the $1.3 billion the company said it has in cash and short-term investments, providing some good news to investors after a rash of setbacks crippled the company’s stock so far this year.

Shares in mortgage companies have been battered over the past few weeks by rising defaults and waning demand among investors for risky subprime loans. Credit Suisse’s bigger credit line will help Fremont exit the mortgage-lending business and allow it to focus more on its commercial lending and its traditional retail banking services through its 22 branches in the state.

This is a rare shot of good news for Fremont, who has been hit hard by the subprime slide, losing more than 63 percent since the beginning of the year.

However, shares in Fremont have gained 56 percent since hitting a 52-week low of $5.55 on March 5.

Shares had gained $1.34, or 18 percent, in afternoon trading Friday on the New york Stock Exchange.