An apparent unidirectional influx constant for manganese as a measure of myocardial calcium channel activity.
OBJECTIVE
To develop an in vivo MR method for evaluation of myocardial calcium channel activity through quantification of apparent unidirectional manganese influx constants following manganese dipyridoxyl-diphosphate (MnDPDP) infusions.


METHODS
A total of 10 healthy volunteers were divided in two groups, and received 5 micromol of MnDPDP per kg of body weight intravenously in a 1.5 Tesla scanner over five or 30 minutes, respectively. A fast inversion recovery gradient echo sequence was used to estimate pre- and postcontrast R1 values and to measure signal changes following infusions. By assuming equal longitudinal relaxivity (r1) of the contrast in all tissue compartments, signal changes in blood and myocardial tissue yielded temporal input and tissue contrast concentrations respectively. Through a two-tissue compartment model, apparent unidirectional influx constants (Ki) for myocardial manganese accumulation were estimated.


RESULTS
Consistent values for Ki in left ventricular wall were found, with a mean value of 5.96 mL/100 g/minute (SD=0.49; N=10). No statistical significant differences in Ki were found between the two infusion groups.


CONCLUSIONS
Since unidirectional manganese accumulation depends upon intact myocyte membranes with functioning calcium channels, the use of unidirectional manganese influx rates may be a valuable research tool for in vivo studies of myocyte functioning in myocardial disease.
Skjold
Arne
A
Department of Circulation and Medical Imaging, Faculty of Medicine, Norwegian University of Science and Technology (NTNU), and Department of Medical Imaging, St. Olavs Hospital, Trondheim, Norway. Arne.Skjold@stolav.no
Kristoffersen
Anders
A
Vangberg
Torgil R
TR
Haraldseth
Olav
O
Jynge
Per
P
Larsson
Henrik B W
HB
D000328:Adult; D015220:Calcium Channels / Q000378:metabolism*; D003287:Contrast Media / Q000493:pharmacokinetics; D017352:Echo-Planar Imaging / Q000379:methods*; D004492:Edetic Acid / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D015640:Ion Channel Gating / Q000502:physiology*; D007700:Kinetics; D008297:Male; D008657:Metabolic Clearance Rate; D009206:Myocardium / Q000378:metabolism*; D011732:Pyridoxal Phosphate / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D012016:Reference Values
D015220:Calcium Channels; D003287:Contrast Media; D019275:Radiopharmaceuticals; D011732:Pyridoxal Phosphate; D004492:Edetic Acid; C060076:N,N'-bis(pyridoxal-5-phosphate)ethylenediamine-N,N'-diacetic acid