(133)Cs+ and (87)Rb+ as NMR active K+ transport analogs: Applications to septic shock

摘要

Proper ion balance between intra- and extracellular compartments is vital for normal physiologic function. However, in pathological states alterations in ion homeostasis (e.g., abnormalities in ion transport processes and intracellular sodium and potassium concentrations) are often observed. One such pathological state is sepsis, the systemic response to severe infection. There is evidence to suggest that disruption of normal Na$sp{+}$/K$sp{+}$ ATPase pump activity may contribute significantly to the pathophysiology of sepsis. As a noninvasive, nondestructive spectroscopic technique, NMR offers a powerful approach to the study of ion balance in intact organ systems during sepsis. Unfortunately, rare NMR active nuclides that are isotopes of the 100% naturally abundant $sp{23}$Na and $sp{39}$K are not available for tracer kinetic studies of Na$sp{+}$ and K$sp{+}$ transport. However, Cs$sp{+}$ is a biologically active analog of K$sp{+}$ and the 100% naturally abundant NMR active $sp{133}$Cs nuclide can be employed to examine K$sp{+}$ transport. The distinguishing feature of $sp{133}$Cs$sp{+}$ is that it naturally gives two separate well-resolved NMR resonances for intra- and extracellular $sp{133}$Cs$sp{+},$ permitting study of the time-course changes of either of these compartments independent of the other. In this thesis, the experimental procedures and compartmental modeling formalisms are developed that allow quantitative analysis of Cs$sp{+}$ membrane transport in the perfused heart from septic and control rats using $sp{133}$Cs NMR. Intracellular $sp{133}$Cs$sp{+}$ is shown to be 100% visible by solution-state NMR methods and its influx transport to be markedly diminished by ouabain, an inhibitor of the Na$sp{+}$/K$sp{+}$ ATPase pump. ($sp{87}$Rb$sp{+}$ NMR studies comparing the transport of the well-accepted K$sp{+}$ analog, Rb$sp{+}$, to that of Cs$sp{+}$ are also presented.) The influx rate constant for Cs$sp{+}$ was decreased by 24% in septic rat hearts, i.e., 0.25 $pm$ 0.07 SD min$sp{-1}$ for controls and 0.19 $pm$ 0.05 SD min$sp{-1}$ for septic, p = 0.02. There was no difference for Cs$sp{+}$ efflux (0.006 $pm$ 0.003 SD min$sp{-1}$ for controls and 0.005 $pm$ 0.002 SD min$sp{-1}$ for septic, p = 0.2). These $sp{133}$Cs$sp{+}$ results are consistent with an inhibition of the Na$sp{+}$/K$sp{+}$ ATPase pump during sepsis/endotoxemia, which may be responsible for, or contribute to, the changes in intracellular Na$sp{+}$ and K$sp{+}$ during the disorder.