Screenscraping a gridview with paging

I have some problems, I must screen scrape a web page that is an aspx-site where the intreseting data is the text in a gridview. I have no problem to get the text from the first page in the gridview.
But how do I get the text from the second page, the third page etc.
The problem is that every page in the gridview has not a specific URL, instead it is a javascript that is executing when I click on the paging linkbutton.
For exempel the javascript for a paging javascript is:
javascript:__doPostBack('ctl00$ctl01$DefaultSiteContentPlaceHolder1$Col1$ucNavBar$rptButtons$ctl02$btnPage','')
How do I simulate this?
This is the code I use to get a webpage for a specific URL:
HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(strUrl); request.Accept = "text/html, application/xhtml+xml, */*"; request.UserAgent = "Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0)"; request.KeepAlive = t ...