With the approval of the commissioner, any banking institution, through action by its board of directors taken at any time and without requiring any action by its stockholders, may issue and sell its capital notes or debentures. All capital notes or debentures are subordinate and subject to the claims of depositors, and at the time of issue may be subordinated and subjected to the claims of other creditors, but in no case may be subject to assessment. The holders of capital notes or debentures as such are not responsible individually for any debts, contracts, or engagements of the issuing institution.