Direct measurement of changes in intracellular calcium transients during hypoxia, ischemia, and reperfusion of the intact mammalian heart.
In studies of ischemia and reperfusion, a major experimental problem has been the inability to measure intracellular ionized calcium ([Ca2+]i) in the intact heart. We have developed a new approach in which the bioluminescent calcium indicator aequorin is used to measure [Ca2+]i in the isolated, coronary-perfused ferret heart. Aequorin is loaded into subepicardial myocytes of the left ventricle, and the signals are recorded simultaneously along with isovolumic left ventricular (LV) pressure at a constant pacing rate. This system shows 1) no attenuation or change of time course of LV pressure development or coronary perfusion pressure after aequorin loading; 2) consistent responses to physiological interventions and drugs; 3) individual aequorin and pressure signals that do not require signal averaging for analysis; and 4) [Ca2+]i levels comparable with those reported in tissue or isolated myocyte cell preparations. During 5 minutes of hypoxia, diastolic [Ca2+]i and LV diastolic pressure increased while the systolic values of both [Ca2+]i and pressure decreased. The peak-to-peak systolic [Ca2+]i versus LV isovolumic pressure relation remained close to the control curve. In contrast, during 3 minutes of global ischemia, LV systolic and diastolic pressures fell rapidly, while [Ca2+]i increased substantially. The [Ca2+]i versus pressure relations for both systole and diastole shifted to the right, indicating desensitization of the contractile apparatus to [Ca2+]i. These results provide evidence that different primary mechanisms determine the systolic and diastolic responses to acute hypoxia versus ischemia. During hypoxia, changes in [Ca2+]i handling probably play a major role, while during ischemia, changes in the Ca2+ sensitivity of the myofilaments appear to be of primary importance in the modulation of contractile dysfunction.
Kihara
Y
Y
Charles A. Dana Research Institute, Boston, Massachusetts.
Grossman
W
W
Morgan
J P
JP
D000331:Aequorin; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003327:Coronary Disease / Q000378:metabolism* / Q000503:physiopathology; D005289:Ferrets; D006439:Hemodynamics; D000860:Hypoxia / Q000378:metabolism* / Q000503:physiopathology; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism*; D007477:Ions; D008297:Male; D015425:Myocardial Reperfusion; D009206:Myocardium / Q000378:metabolism*
D007477:Ions; D000331:Aequorin; D002118:Calcium