Calcium uptake in mitochondria from different skeletal muscle types.
The kinetics of calcium (Ca2+) uptake have been studied in mitochondria isolated from the different types of skeletal muscle. These studies demonstrate that the Ca2+ uptake properties of skeletal mitochondria are similar to those from liver and cardiac mitochondria. The Ca2+ carriers apparently have a high affinity for Ca2+ (Michaelis constants in the microM range). The relationship between Ca2+ uptake and initial Ca2+ concentration (10(-5) to 10(-7) M) is sigmoid in all mitochondria from the different skeletal muscle types suggesting that the uptake process is cooperative. Hill plots reveal coefficients of approximately 2 for mitochondria from fast-twitch muscle and 3.5 for slow-twitch muscle, adding further evidence to the concept that the uptake process is cooperative. An analysis of the potential role of mitochondria in the sequestration of Ca2+ during muscular contraction demonstrated that mitochondria from slow-twitch muscle of both rats and rabbits can potentially account for 100% of the relaxation rate at a low frequency of stimulation (5 Hz). In fast-twitch muscle, the mitochondria appear unable to play a significant role in muscle relaxation, particularly at stimulation frequencies that are considered in the normal physiological range. In summary, it appears that Ca2+ uptake by mitochondria from slow-twitch skeletal muscle has kinetic characteristics which make it important as a potential regulator of Ca2+ within the muscle cell under normal physiological conditions.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005260:Female; D007700:Kinetics; D008297:Male; D008931:Mitochondria, Muscle / Q000378:metabolism*; D009119:Muscle Contraction; D009132:Muscles / Q000502:physiology* / Q000648:ultrastructure; D011817:Rabbits; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
D002118:Calcium