Subcellular localization of calcium release in isolated rat myocardial cells.
Independent determinations of Ca2+ by two indicators showed that subcellular Ca2+ activity (intracellular free calcium concentration) was heterogeneous in rat myocardial cells. Arsenazo III (Az III), a membrane-impermeant absorbance indicator for Ca2+, was loaded into cardiac muscle via liposomes and calcium quantitated at two wavelengths through a focal point diaphragm in 5-100 microns 2 regions by a photometer. Fura-2, a high-affinity fluorescent calcium indicator, was loaded into cells as the ester form, and the light intensity was measured by digital-imaging microscopy using a photon-counting camera. Calcium activity at each picture element was quantitated by division of fluorescence excited by two ultraviolet wavelengths, and corrected for concentration differences in fura-2 by a third, Ca(2+)-insensitive wavelength. Both methods revealed hot spots of Ca2+ release and uptake that could be enlarged, added to, or altered. Addition of 1-10 nM norepinephrine caused up to a 500% increase in Ca2+ in localized regions, although whole cell average Ca2+ increased by only 0-80%, suggesting the importance of localized intracellular Ca2+ release for contraction.
Hermsmeyer
K
K
Chiles Research Institute, Providence Medical Center, Portland, OR 97213.
Mason
R
R
Puga
A
A
Erne
P
P
D000818:Animals; D001150:Arsenazo III / Q000008:administration & dosage / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D016257:Fura-2 / Q000008:administration & dosage / Q000494:pharmacology; D008081:Liposomes; D008855:Microscopy, Electron, Scanning; D009206:Myocardium / Q000378:metabolism / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000378:metabolism*
D008081:Liposomes; D001150:Arsenazo III; D002118:Calcium; D016257:Fura-2