The effects of exogenous calcium buffers on the systolic calcium transient in rat ventricular myocytes.
The aim of this work was to characterize the effects that two commonly used "caged" calcium buffers (NP-EGTA and nitr-5) have on the amplitude and time course of decay of the calcium transient. We made quantitative measurements of both free and total calcium using the measured buffering properties of the cell. Intracellular calcium concentration ([Ca(2+)](i)) was measured with fluo-3 in rat ventricular myocytes. Incorporation of the buffer NP-EGTA decreased both the amplitude and rate of decay of the caffeine response. The slowing could be quantitatively accounted for by the measured increased buffering. These effects were removed by photolysis of NP-EGTA. Similar results were obtained with nitr-5 except that the effects were not completely removed by photolysis. This was shown to be due to the persistence of a component of the increased buffering after photolysis. Both buffers decreased the amplitude of the systolic calcium transient. However, although nitr-5 produced a simple slowing of the decay, NP-EGTA resulted in an initial rapid phase of decay. This rapid phase of decay is attributed to calcium binding to NP-EGTA. This work represents the first quantitative analysis of the effects that extra buffering by a fast and a slow calcium chelator may have on the calcium transient.
Unit of Cardiac Physiology, Department of Medicine, The University of Manchester, Manchester M13 9PT, United Kingdom. mary.e.diaz@man.ac.uk
M E
ME
Díaz
A W
AW
Trafford
D A
DA
Eisner
D000814:Aniline Compounds / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002478:Cells, Cultured; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D008027:Light; D008956:Models, Chemical; D009132:Muscles / Q000166:cytology / Q000378:metabolism; D009206:Myocardium / Q000166:cytology; D018408:Patch-Clamp Techniques; D010782:Photolysis; D051381:Rats; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D014966:Xanthenes / Q000494:pharmacology
D000814:Aniline Compounds; D000697:Central Nervous System Stimulants; D002614:Chelating Agents; D014966:Xanthenes; C052455:nitr 5; C059715:Fluo-3; D002110:Caffeine; D004533:Egtazic Acid; D002118:Calcium