Calcium paradox in newborn and adult guinea-pig hearts: changes in intracellular taurine and the effects of extracellular magnesium.
The isolated hearts of adult and neonatal guinea-pigs have been compared for changes in intracellular amino acids during calcium depletion and the loss of cellular proteins on calcium repletion. Taurine, in freshly excised ventricles of neonatal guinea-pig heart, at 10.5 +/- 0.5 mmol (kg wet weight)-1 (n = 5) is less than in the adult heart (13.0 +/- 0.6 mmol (kg wet weight)-1 (n = 5)) but still is the most abundant amino acid free in the sarcoplasm. A marked loss of tissue taurine in both neonatal and adult hearts (a fall to 3.5 +/- 0.25 mmol (kg wet weight)-1 in neonatal and 4.9 +/- 0.6 mmol (kg wet weight)-1 in adult hearts after 10 min) was induced by perfusion with Ca, Mg-free Tyrode solution. A fall in several of the alpha-amino acids was also seen during this manoeuvre. On reperfusion with normal Tyrode solution, a marked release of proteins (lactate dehydrogenase, creatine kinase and myoglobin) was observed, which showed a similar time course in both types of heart. Elevation of [Mg]o during calcium depletion reduced protein loss on calcium repletion in both neonatal and adult guinea-pig hearts. This effect was consistent with an effect of Mg2+ on the rise of [Na]i. A second effect of [Mg]o was to shift the time to peak protein loss, an effect greater in neonatal hearts and more pronounced for the proteins with larger molecular weight (lactate dehydrogenase > creatine kinase > myoglobin). This latter effect of Mg2+ would seem not to be due to an effect on capillary permeability because the presence of bovine serum albumin in the perfusate failed to produce a similar effect. Neonatal and adult guinea-pig hearts show a similar sensitivity to the calcium paradox and similar changes in tissue taurine during calcium depletion, and therefore contrast with rat and rabbit heart.
Department of Physiology, School of Veterinary Science, University of Bristol.
M S
MS
Suleiman
R A
RA
Chapman
D000375:Aging / Q000378:metabolism* / Q000502:physiology; D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology / Q000502:physiology; D003402:Creatine Kinase / Q000378:metabolism; D006168:Guinea Pigs; D006321:Heart / Q000502:physiology*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology*; D009206:Myocardium / Q000737:chemistry / Q000378:metabolism*; D009211:Myoglobin / Q000378:metabolism; D013654:Taurine / Q000032:analysis / Q000378:metabolism*; D013997:Time Factors
D009211:Myoglobin; D013654:Taurine; D007770:L-Lactate Dehydrogenase; D003402:Creatine Kinase; D008274:Magnesium; D002118:Calcium