  In a recent letter Johnson and Payne (JP) have studied the effect of the
electron interaction on the periodic conductance oscillations in narrow
channels based on an exactly solvable model. In this Comment we discuss the
exchange-correlation effect on JP's model using a solvable electron model. We
wish to point out that when the interaction strength becomes rather small,
there may appear two periods in the conductance oscillations due to the
exchange effect.
