Ionic movements mediated by monensin in frog skeletal muscle.
Monensin-mediated ionic movements were studied in frog skeletal muscle. The ionophore, which forms electrically neutral complexes with monovalent cations, induced dose dependent fluxes of Na+, K+ and H+ in and out of the fibers. Monensin concentrations ([MON]) ranged from 2 to 40 microM. In the presence of normal Ringer's solution the following maximum ionic exchanges were generated by monensin (in pmol cm-2 s-1): (1) Nai+/Nao+ 112, (2) Nai+/Ho+ 30.7, (3) Ki+/Nao+ 14.2 (4) Hi+/Nao+ 49. The maximum net fluxes produced by these exchanges (i.e. for [MON] = infinity) are (in pmol cm-2 s-1): Na+ (inward) 32.5, K+ (outward) 14.2, H+ (outward) 18.3. The last one appears to be largely offset by a passive (monensin-independent) H+ influx down an inwardly directed electrochemical gradient promoted by pH reduction of the T-tubular lumen content as a consequence of the monensin-mediated net H+ efflux. Maximum unidirectional cationic fluxes mediated by monensin amounted to 206 pmol cm-2 s-1 and had the following composition: influx: 85% Na+ and 15% H+; efflux: 69% Na+, 7% K+, 24% H+.
Hoya
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Catedra de Fisiologia con Biofisica, Facultad de Ciencias Medicas, Universidad Nacional de La Plata, Argentina.
Venosa
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RA
D000818:Animals; D001001:Anura; D001692:Biological Transport; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008985:Monensin / Q000494:pharmacology*; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
D008985:Monensin; D012964:Sodium