Mechanisms of passive potassium influx in corn mitochondria.

Corn mitochondria in 100 millimolar KCl show accelerated passive swelling upon addition of uncoupler. This unusual response has been compared with swelling produced by valinomycin, tripropyltin, and nigericin. It is concluded that the driving force for swelling lies with the chloride gradient and a high P(Cl):P(K) ratio, the chloride influx creating a negative membrane potential. The action of uncoupler is to facilitate K(+) influx via the endogenous H(+)/K(+) antiporter. The antiporter is active over the pH range 6 to 8, is not sensitive to Mg(2+) concentration, and is not inactivated by aging. It is not clear why corn mitochondria show this exceptional activity of the H(+)/K(+) antiporter in K(+) influx. It is speculated that during isolation the antiporter may be exposed or activated, and that it contributes to cyclic K(+) transport and high State 4 respiration rates.