Effect of inotropic stimulation on cytosolic mg2+ in isolated rat heart: a 31p magnetic resonance study

✍ Scribed by John P Headrick; Roger J. Willis

• Publisher: John Wiley and Sons
• Year: 1989
• Tongue: English
• Weight: 595 KB
• Volume: 12
• Category: Article
• ISSN: 0740-3194
• DOI: 10.1002/mrm.1910120305

✦ Synopsis

Alterations in cytosolic metabolites and [ Mg2+], were monitored using 3'P magnetic resonance spectroscopy during inotropic stimulation of isolated rat heart [ 10 nMisoproterenol, 0.6 p M isobutyl-1-methylxanthine (IBMX), 5 pM ouabain]. All drugs significantly elevated contractile function (rate-pressure product) and MV02 by approximately 100-150% ( P < 0.001 ), decreased cytosolic [creatine phosphate] ([CrP]) and

[ATP] (approximately 65 and 80% of control values, respectively) ( P < 0.001), increased [ Pr ] to more than 180% of pretreatment values, and decreased [ H + 1 by less than 15% (P < 0.05 ) . A significant relative shift in the a-P and 8-P resonances of ATP (P < 0.0 1 ) occurred with inotropic stimulation. [ Mg2+], calculated on the basis of these shifts was found to be 0.78 k 0.1 m M in control hearts, and increased to maxima of 1.9 k 0.2,2.0 -+ 0.2, and 2.9 f 0.2 mMduring infusion ofisoproterenol, IBMX, and ouabain, respectively. Changes in [ Mg2+], correlate with cytosolic [ATP] + [CrP] in all hearts ( r = 0.89, 0.91, and 0.88 in isoproterenol-, IBMX-, and ouabain-treated hearts, respectively). The significantly higher [ Mg"], with ouabain infusion (P < 0.01 ) at similar workloads and [ ATP] + [CrP] supports the proposal that a ouabain-inhibited Mg" pump exists in the plasma membrane. The data support acute changes in [ Mg2+] I during alterations in inotropic state that may be important in modulating metabolic and contractile function.