Direct recording of EDP-EDV relationship in isolated rat left ventricle: effect of diastolic crossbridge formation.
OBJECTIVE
The aim was to investigate whether the end diastolic pressure-end diastolic volume (EDP-EDV) relationship of the left ventricle can be influenced by calcium dependent elements, especially at low values of end diastolic pressure.


METHODS
Isolated rat hearts were perfused in a modified Langendorff perfusion system. The EDP-EDV relationship of the left ventricle was investigated. Pressure was recorded with a microtip pressure catheter and volume with a microconductance catheter. Crossbridge cycling was affected by adding calcium antagonists (verapamil, diltiazem, nifedipine at 2.10(-7) M) or by adding the Mg-ATPase blocker BDM (2,3-butanedione-2-monoxime, 10(-3) M) to the perfusate.


RESULTS
The above had a negative inotropic effect in systole. At EDP = 0 after stimulation the active isovolumetric pressure was zero. In diastole, BDM shifted the EDP-EDV relationship to slightly smaller EDVs. A decrease of about 5% in the EDV was found at lower EDP values. Ca2+ antagonists increased the EDV up to 40-80% at low EDP values. At higher EDP values only a small increase of EDV (about 10%) was found after verapamil perfusion. The results obtained are interpreted in terms of a three step crossbridge model.


CONCLUSIONS
At low EDP, diastolic volume is dependent upon weakly bound crossbridges as a function of the [Ca2+] in the cardiac cell.
Faculty of Medicine, Department of Medical Physiology and Sports Medicine, University of Utrecht, The Netherlands.
P
P
Schiereck
R
R
Hoefnagel
E L
EL
De Beer
B G
BG
Van Heijst
W L
WL
Mosterd
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D003931:Diacetyl / Q000031:analogs & derivatives / Q000494:pharmacology; D003971:Diastole; D004110:Diltiazem / Q000494:pharmacology; D006352:Heart Ventricles / Q000378:metabolism; D009543:Nifedipine / Q000494:pharmacology; D010477:Perfusion; D051381:Rats; D011921:Rats, Inbred WKY; D013318:Stroke Volume / Q000187:drug effects*; D016277:Ventricular Function, Left / Q000187:drug effects*; D014700:Verapamil / Q000494:pharmacology
D002121:Calcium Channel Blockers; C004717:diacetylmonoxime; D014700:Verapamil; D004110:Diltiazem; D009543:Nifedipine; D003931:Diacetyl; D002118:Calcium