Except as provided in § 616 of this title, no shareholder of a professional corporation may sell or transfer such shareholder's shares in the professional corporation, except to the professional corporation, or to another individual who is eligible to be a shareholder of such professional corporation. Unless the certificate of incorporation or bylaws of a professional corporation, or a separate contract among all of the shareholders of the professional corporation, provides otherwise for the manner in which such sale or transfer of shares as permitted under this section is to take place, the sale or transfer may be made only after the same shall have been approved, at a stockholders' meeting specially called for such purpose, or at an annual meeting with 10 days' notice of such additional purpose, by such proportion, not less than a majority, of the outstanding stock entitled to be voted on that question as may be provided in the certificate of incorporation or in the bylaws. At such shareholders' meeting the shares of stock held by the shareholder proposing to sell or transfer such shareholder's shares may not be voted or counted for any purpose. The certificate of incorporation may provide specifically for additional restraints on the alienation of shares, including the redemption or purchase of such shares by the professional corporation at prices and in a specific manner, or the bylaws of the professional corporation, or a separate contract among all of the shareholders of the professional corporation and, if such contract provides for redemption, the professional corporation itself, may provide for such restraints on alienation of shares including the prices and manner of redemption or purchase as permitted under this section; provided, however, such provisions, dealing with the purchase or redemption by the professional corporation of its shares, may not be invoked at a time or in a manner that would impair the capital of the professional corporation.