OSMOTIC EFFECTS ON MITOCHONDRIA FROM 2 SPECIES OF AMPHIBIAN, BUFO-MARINUS AND RANA-CATESBEIANA

The effects of ionic and/or osmotic change on skeletal muscle mitochondrial performance were investigated. Two substrates, pyruvate and glutamate, and variation in osmotic pressure from 205 to 360 mosm in KCl or mannitol/sucrose media had no effect on maximal respiratory rate (state 3) or coupling (respiratory control ratio) in either species. Over an equivalent range of osmolalities associated with dehydration, organismic maximal O2-consumption rates are severely diminished with increasing osmolalities. The data do not support a mitochondrial limit to organismic O2 consumption under dehydration. There were interspecies differences in state 3 respiration and coupling that were similar to differences noted in mitochondria isolated from fish red and white muscle, with toad mitochondria behaving more like red muscle and frog mitochondria behaving more like white muscle.