Adaptation of single cardiac ryanodine receptor channels.
Single cardiac ryanodine receptor (RyR) channel adaptation was previously defined with Ca2+ stimuli produced by flash photolysis of DM-nitrophen (caged-Ca+2). Photolysis of DM-nitrophen induced a very fast Ca+2 overshoot (Ca+2 spike) at the leading edge of the Ca+2 stimuli. It has been suggested that adaptation (tau approximately 1.3 s) may reflect Ca+2 slowly coming off the RyR Ca+2 activation sites following the faster Ca+2 spike (tau approximately 1 ms). This concern was addressed by defining the Ca2+ deactivation kinetics of single RyR channels in response to a rapid reduction in free Ca2+ concentration ([Ca2+]FREE). The [Ca2+]FREE was lowered by photolysis of Diazo-2. Single RyR channels deactivated (tau approximately 5.3 ms) quickly in response to the photolytically induced [Ca2+]FREE reduction. Improved estimates of the Ca2+ spike time course indicate that the Ca2+ spike is considerably faster (10-100-fold) than previously thought. Our data suggest that single RyRs are not significantly activated by fast Ca2+ spikes and that RyR adaptation is not due to deactivation following the fast Ca2+ spike. Thus, RyR adaptation may have an important impact on Ca2+ signaling in heart.
Vélez
P
P
Loyola University Chicago, Maywood, Illinois 60153, USA. pvelez@luc.edu
Györke
S
S
Escobar
A L
AL
Vergara
J
J
Fill
M
M
D000085:Acetates; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D002614:Chelating Agents; D003979:Diazonium Compounds; D004285:Dogs; D005029:Ethylenediamines; D066298:In Vitro Techniques; D007700:Kinetics; D008051:Lipid Bilayers / Q000378:metabolism; D009124:Muscle Proteins / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010642:Phenoxyacetates; D010743:Phospholipids / Q000378:metabolism; D010782:Photolysis; D019837:Ryanodine Receptor Calcium Release Channel; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D015398:Signal Transduction
D000085:Acetates; D015220:Calcium Channels; D002614:Chelating Agents; D003979:Diazonium Compounds; D005029:Ethylenediamines; D008051:Lipid Bilayers; D009124:Muscle Proteins; D010642:Phenoxyacetates; D010743:Phospholipids; D019837:Ryanodine Receptor Calcium Release Channel; C063685:diazo-2; C057014:DM-nitrophen; D002118:Calcium