ASP.NET unable to select node using SelectSingleNode method with namespace manager

What namespace should I configure to read Google shopping feed? And then how do I select a value using ASP.NET? I can't seem to select the value for node g:google_product_category

My Google feed (some nodes omitted for overview)

<?xml version="1.0" encoding="utf-8"?>
<rss version="2.0" xmlns:g="http://base.google.com/ns/1.0">
    <channel>
        <title><![CDATA[Foo]]></title>
        <link>http://www.foo.com/</link>
        <description><![CDATA[]]></description>
        <item>
            <g:id>10580119</g:id>
            <title><![CDATA[Some title]]></title>
            <g:google_product_category><![CDATA[Bags]]></g:google_product_category>
        </item>
    </channel>
</rss>      

My code

Dim productXML As New XmlDocument
Dim root As XmlNode
Dim node As XmlNode

productXML.LoadXml(responseString) 'responseString contains the full Google feed
Dim nodeList As XmlNodeList = root.SelectNodes("/rss/channel/item")

Dim mgr As XmlNamespaceManager = New XmlNamespaceManager(productXML.NameTable)
mgr.AddNamespace("g", productXML.DocumentElement.NamespaceURI)

'here a nodeList.Count call returns the correct number of products, so I'm able to read some items

For Each node In nodeList

If node.SelectSingleNode("g:google_product_category", mgr) IsNot Nothing Then 'what should I add here?!

productXML.DocumentElement.NamespaceURI does not correspond to "http://base.google.com/ns/1.0", so set it as

mgr.AddNamespace("g", "http://base.google.com/ns/1.0")

or use node.Item

Dim productXML As New XmlDocument
Dim node As XmlNode

productXML.LoadXml(responseString)

Dim mgr As XmlNamespaceManager = New XmlNamespaceManager(productXML.NameTable)
mgr.AddNamespace("g", productXML.DocumentElement.NamespaceURI)

Dim root As XmlElement = productXML.DocumentElement
Dim nodeList As XmlNodeList = root.SelectNodes("/rss/channel/item", mgr)

For Each node In nodeList
    If node.Item("g:google_product_category") IsNot Nothing Then
        Console.WriteLine(node.Item("g:google_product_category").InnerXml)
    End If
Next