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Calcium transients caused by calcium entry are influenced by the sarcoplasmic reticulum in guinea‐pig atrial myocytes.
Author(s) -
Lipp P,
Pott L,
Callewaert G,
Carmeliet E
Publication year - 1992
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1992.sp019266
Subject(s) - calcium , endoplasmic reticulum , myocyte , ryanodine receptor 2 , guinea pig , atrial myocytes , sarcoplasm , chemistry , biophysics , medicine , ryanodine receptor , biology , endocrinology , biochemistry
1. Single atrial myocytes obtained by enzyme perfusion from hearts of adult guinea‐pigs were investigated using whole‐cell voltage clamp and Indo‐1 micro‐fluorometry. 2. In myocytes loaded with a solution containing citrate as a low‐affinity, non‐saturable Ca2+ chelator, two types of [Ca2+]i transients could be recorded during repetitive activation of L‐type Ca2+ current. Both large and small [Ca2+]i transients occurred; large transients reached peak values of about 1 microM, and small transients were about 100 nM or less in amplitude. 3. In the case of the large transients, peak [Ca2+]i was usually reached with a variable delay after repolarization from a voltage step that activated calcium current (ICa). For the small transients the rise in [Ca2+]i paralleled ICa. Upon repolarization [Ca2+]i started to decay. 4. The small transients reflect entry of Ca2+ through Ca2+ channels (entry transients), whereas the large transients are due to entry and release from the sarcoplasmic reticulum (release transients). 5. The entry transients displayed a positive staircase pattern during trains of depolarizing voltage steps despite constant or even decreasing amplitude of ICa. The steepness of the staircase was increased by elevation of [Ca2+]o. Entry transients were always smallest immediately after a release transient. 6. After functional removal of the sarcoplasmic reticulum by caffeine (1‐5 mM) the staircase pattern of the transients reflecting Ca2+ entry was abolished. 7. It is concluded that the staircase pattern is due to rapid uptake by the sarcoplasmic reticulum of Ca2+ entering the cell, resulting in an attenuation of the signal. The attenuation is strongest shortly after a release signal, when the rate of sequestration of Ca2+ by the SR should be highest. 8. Evidence is provided that a compartment of the SR is involved in attenuation of the entry transients. This compartment has been identified recently as a peripheral release compartment.