title: The permeability of uncoupled heart mitochondria to potassium ion.
abstract: Isolated heart mitochondria retain matrix K+ in a K+-free medium and exchange matrix 42K+ with external K+ only slowly. This low permeability to K+ is maintained when the proton motive force is dissipated by addition of an uncoupler, but can be increased markedly in uncoupled mitochondria when (a) NADPH becomes oxidized and (b) a Ca2+ chelator or ruthenium red is added (Jung, D. W., and Brierley , G. P. (1981) J. Biol. Chem. 256, 10490-10496). This latter requirement suggests that decreased Ca2+ binding or alteration of the Ca2+ uniporter may be involved in the induction of permeability to K+ in these mitochondria. The present studies establish that La3+ (k0.5 = 1.8 nmol X mg-1 of protein) also induces K+ permeability in uncoupled mitochondria in which NADPH has been oxidized. The amount of net K+ loss or passive 42K+/K+ exchange induced by La3+ corresponds to that produced by ruthenium red or EGTA and appears to vary from preparation to preparation as a function of the endogenous adenine nucleotide (AN) content of the mitochondria. The permeability to K+ induced by all three reagents is increased by depletion of endogenous AN with PPi and strongly inhibited by low levels of exogenous AN. The optimum passive permeability to K+ develops at pH 7.5, is inhibited by Nupercaine , quinine, and dicyclohexylcarbodiimide, and is increased in a sucrose, as opposed to a KCl medium. The increased permeability to K+ appears to result from the opening of one or more K+-conducting uniport pathways, rather than K+/H+ exchange. Since Ca2+ efflux remains sensitive to ruthenium red when K+ efflux is induced, it seems unlikely that the Ca2+ uniporter itself can provide a pathway for K+ flux. The presence of such latent pathways for passive K+ permeability must be considered when defining the properties of the putative K+/H+ antiporter and during isolation and reconstitution protocols involving mitochondrial K+ transport components.
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D015220:Calcium Channels; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002417:Cattle; D004533:Egtazic Acid / Q000378:metabolism; D007473:Ion Channels / Q000378:metabolism*; D007811:Lanthanum / Q000378:metabolism; D008929:Mitochondria, Heart / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D010539:Permeability; D011188:Potassium / Q000378:metabolism*; D012430:Ruthenium Red / Q000378:metabolism; D013395:Sucrose / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D007473:Ion Channels; C034703:mitochondrial calcium uniporter; D012430:Ruthenium Red; D004533:Egtazic Acid; D009249:NADP; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D013395:Sucrose; D000244:Adenosine Diphosphate; D007811:Lanthanum; D011188:Potassium