RESUMO
The conditions of potassium transport were investigated in isolated rabbit hear mitochondria. In the presence of 5 to 40 mM potassium chloride there is a rapid initial phase of potassium influx of less than 2 min duration in which 65-75% of the total K+ uptake occurs. This is followed by a slow phase of K+ uptake of about 45 min during which 25 to 35% of the total potassium was taken up. While the rapid phase is due to passive diffusion, the slow phase is an active process which requires either ATP or respiratory substrates as an energy source. It can be totally abolished by 0.5 mM antimycin A. An increase of the calcium concentration in the incubation medium to more than 5 X 10(-5)M resulted in an inhibition of the energy-dependent uptake of potassium which was directly proportional to the calcium level. k-Strophanthin induced a distinct inhibition only at very high concentration (greater than 10(-4)M). The inhibition of potassium uptake by 1. 3 or 5 mM calcium chloride was gradually cancelled by increasing k-strophanthin concentrations above 10(-8)M. Maximal cancellation was found with 10(-5)M of k-strophanthin. This concentration almost completely prevented the inhibition by calcium ions. On the other hand, 10(-5)M k-strophanthin had no inhibitory effect on the energy-dependent uptake of 0.5 mumoles of calcium chloride or on the oxidative phosphorylation of 0.5 mumoles of ADP added to the incubation medium.
