Changes in Calcium Uptake Rate by Rat Cardiac Mitochondria during Postnatal Development

Abstract Ca 2+ uptake, transmembrane electrical potential (Δ ψ m) and oxygen consumption were measured in isolated ventricular mitochondria of rats from 3 days to 5 months of age. Estimated values of ruthenium red-sensitive, succinate-supported maximal rate of Ca 2+ uptake (V max , expressed as nmol Ca 2+ /min/mg protein) were higher in neonates and gradually fell during postnatal development (from 435±24 at 3–6 days, to 156±10 in adults, P 0.5 values (10 μ m ) were not significantly affected by age. Under similar conditions, mitochondria from adults (5 months old) and neonates (4–6 days old) showed comparable state 4 (succinate and α -ketoglutarate as substrates) and state 3 ADP ( α -ketoglutarate-supported) respiration rates, as well as Δ ψ m values (−150 mV). Respiration-indpendent Δ ψ m and Ca 2+ uptake, supported by valinomycin-induced K + efflux were also investigated at these ages. A transient Δ ψ m (−30 mV) was evoked by valinomycin in both neonatal and adult mitochondria. Respiration-independent Ca 2+ uptake was also transient, but its initial rate was significantly higher in neonates than in adults (49.4±10.0 v 28.0±5.7 mmol Ca 2+ /min/mg protein, P 2+ uptake capacity of rat cardiac mitochondria is remarkably high just after birth and declines over the first weeks of postnatal life, without change in apparent affinity of the transporter. Increased mitochondrial Ca 2+ uptake rate in neonates appears to be related to the uniporter itself, rather than to modification of the driving force of the transport.