why grid view doesnt go to invisible mode

Question

I have following Query y my GridView is not go to invisible on selected index change of course please et me know this is my code

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        FillYear();
        FillCompany();
        FillCourseName();
    }
    Util.JQueryUtils.RegisterTextBoxForDatePicker(Page, vistDate);
    gridNotExist.Text = "";
    noRecordExistOnOkButton.Text = "";
    Btnsave.Visible = false;
    GridView1.Visible = false;
}

this is selecteed index change for course

protected void course_SelectedIndexChanged(object sender, EventArgs e)
{
    try
    {
        int courseId = Convert.ToInt32(course.SelectedValue);
        DataTable dt = placementManager.GetBranchList(courseId);
        if (dt.Rows.Count != 0)
        {
            Branch.DataSource = dt;
            Branch.DataTextField = "branch_name";
            Branch.DataValueField = "branch_id";
            Branch.DataBind();                
        }
    }
    catch (Exception ex)
    {
        COMMON.logger.Error("Error on course_SelectedIndexChanged:CompanySelected.aspx.cs", ex);
    } 
}

Above is my code which once generated grid view doesn't make to invisible mode in course selected index change. while i seen by applying break point that it first hit to page load event then hit course slccted index change event so by inferring code i think it should go invisible and save button too but it doesn't go