M Ritter1, Z Su, A Yao, I Zubair, S Xu, J Shelby, W H Barry. 1. Division of Cardiology, University of Utah Health Sciences Center, 50 North Medical Drive, Salt Lake City, UT 84132, USA.
Abstract
BACKGROUND: Recent studies from our laboratory have demonstrated that in vivo contractile function of rejecting mouse heterotopic abdominal heart allografts 5 days after transplantation is depressed to 40% of that of syngenic controls, and that this depression of function is prevented by the nitric oxide synthase (NOS) inhibitor NG-monomethyl-l-arginine. However, the mechanisms of altered myocyte function caused by nitric oxide production in this setting are not established. METHODS: We measured intracellular calcium concentration ([Ca2+]i) transients (fluo-3, confocal microscopy), fractional shortening (video motion), and L-type Ca2+ currents (whole-cell patch clamp) 5 days after transplantation in ventricular myocytes freshly isolated from syngenic (Balb/C into Balb/C) and allogenic (Balb/C into C3H) transplants. RESULTS: L-type Ca2+ currents, [Ca2+]i transient amplitudes, and fractional shortening did not differ between nonrejecting, syngenic and rejecting, allogenic transplants. Catecholamine responsiveness as analyzed by the change in the peak [Ca2+]i transient induced by 100 nM isoproterenol was also similar. Superfusion with l-arginine, an NOS substrate, caused decreased shortening with no change in [Ca2+]i transients in allogenic myocytes, but had no effect in syngenic myocytes. CONCLUSIONS: Depressed contractile function of rejecting allogenic heart transplants in vivo appears to be caused in part by an NOS-dependent decrease in myofilament Ca2+ sensitivity.
BACKGROUND: Recent studies from our laboratory have demonstrated that in vivo contractile function of rejecting mouse heterotopic abdominal heart allografts 5 days after transplantation is depressed to 40% of that of syngenic controls, and that this depression of function is prevented by the nitric oxide synthase (NOS) inhibitor NG-monomethyl-l-arginine. However, the mechanisms of altered myocyte function caused by nitric oxide production in this setting are not established. METHODS: We measured intracellular calcium concentration ([Ca2+]i) transients (fluo-3, confocal microscopy), fractional shortening (video motion), and L-type Ca2+ currents (whole-cell patch clamp) 5 days after transplantation in ventricular myocytes freshly isolated from syngenic (Balb/C into Balb/C) and allogenic (Balb/C into C3H) transplants. RESULTS: L-type Ca2+ currents, [Ca2+]i transient amplitudes, and fractional shortening did not differ between nonrejecting, syngenic and rejecting, allogenic transplants. Catecholamine responsiveness as analyzed by the change in the peak [Ca2+]i transient induced by 100 nM isoproterenol was also similar. Superfusion with l-arginine, an NOS substrate, caused decreased shortening with no change in [Ca2+]i transients in allogenic myocytes, but had no effect in syngenic myocytes. CONCLUSIONS: Depressed contractile function of rejecting allogenic heart transplants in vivo appears to be caused in part by an NOS-dependent decrease in myofilament Ca2+ sensitivity.