Metabolic inhibition alters subcellular calcium release patterns in rat ventricular myocytes: implications for defective excitation-contraction coupling during cardiac ischemia and failure.
Metabolic inhibition (MI) contributes to contractile failure during cardiac ischemia and systolic heart failure, in part due to decreased excitation-contraction (E-C) coupling gain. To investigate the underlying mechanism, we studied subcellular Ca2+ release patterns in whole cell patch clamped rat ventricular myocytes using two-dimensional high-speed laser scanning confocal microscopy. In cells loaded with the Ca2+ buffer EGTA (5 mmol/L) and the fluorescent Ca2+-indicator fluo-3 (1 mmol/L), depolarization from -40 to 0 mV elicited a striped pattern of Ca2+ release. This pattern represents the simultaneous activation of multiple Ca2+ release sites along transverse-tubules. During inhibition of both oxidative and glycolytic metabolism using carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP, 50 nmol/L) and 2-deoxyglucose (2-DG, 10 mmol/L), there was a decrease in inward Ca2+ current (ICa), the spatially averaged Ca2+ transient, and E-C coupling gain, but no reduction in sarcoplasmic reticulum Ca2+ content. The striped pattern of subcellular Ca2+ release became fractured, or disappeared altogether, corresponding to a marked decrease in the area of the cell exhibiting organized Ca2+ release. There was no significant change in the intensity or kinetics of local Ca2+ release. The mechanism is not fully explained by dephosphorylation of L-type Ca2+ channels, because a similar degree of ICa"rundown" in control cells did NOT result in fracturing of the Ca2+ release pattern. We conclude that metabolic inhibition interferes with E-C coupling by (1) reducing trigger Ca2+, and (2) directly inhibiting sarcoplasmic reticulum Ca2+ release site open probability.
Fukumoto
Gary H
GH
Department of Medicine, Cardiovascular Research Laboratories, Geffen School of Medicine at UCLA, Los Angeles, Calif 90095-1679, USA.
Lamp
Scott T
ST
Motter
Christi
C
Bridge
John H B
JH
Garfinkel
Alan
A
Goldhaber
Joshua I
JI
D000332:Aerobiosis / Q000187:drug effects*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology*; D002478:Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D003847:Deoxyglucose / Q000494:pharmacology*; D006019:Glycolysis / Q000187:drug effects*; D006333:Heart Failure / Q000378:metabolism*; D006352:Heart Ventricles / Q000166:cytology; D017136:Ion Transport / Q000187:drug effects; D018613:Microscopy, Confocal; D017202:Myocardial Ischemia / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism
D020746:Calcium Channels, L-Type; D019837:Ryanodine Receptor Calcium Release Channel; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D003847:Deoxyglucose; D012964:Sodium; D002118:Calcium