31P magnetization transfer studies of creatine kinase kinetics in living rabbit brain

Abstract

The kinetics of the CK reaction in the living rabbit brain was studied by three ³¹P magnetization transfer methods: inversion recovery (IR), inversion transfer (IT), and steadystate saturation transfer (SSST). Longitudinal relaxation rates (T⁻¹) were determined from IR and IT experiments. The values were 0.88 ± 0.08 s⁻¹ for PCr and 2.45 ± 0.39 s⁻¹ for γ-ATP. Analysis of the results of SSST experiments in which γ-ATP was saturated yielded a forward rate constant k_F of 0.53 ± 0.07 s⁻¹. Upon saturation of PCr no change in the γ-ATP signal could be detected in SSST. An average reverse rate constant (k_R ± S.D.) of 0.52 ± 0.04 s⁻¹ was estimated by analyzing IT data from three experiments with selective inversion of γ-ATP. The standard error of k_R was 50%. The average [PCr]/[ATP] of 1.21 ± 0.16 together with the values of k_F and k_R yielded a forward-to-reverse flux ratio of 1.23. Within our limits of accuracy this ratio was not significantly different from 1.0, thus suggesting that in the brain the forward and reverse CK fluxes are equal. © 1987 Academic Press, Inc.