Inositol tetrakisphosphate stimulates a novel ATP-independent Ca2+ uptake mechanism in cardiac junctional sarcoplasmic reticulum.
The effects of inositol phosphates on Ca2+ uptake in cardiac junctional sarcoplasmic reticulum (JSR) vesicles was investigated. Inositol 1,3,4,5-tetrakisphosphate (IP4) selectively increased Ca2+ uptake 2.8 fold over basal levels whereas 1,3,4-IP3, 1,4,5-IP3 or 1,4-IP2 were without effect. Stimulation of Ca2+ uptake by IP4 was maximal within 15-60 sec at 30 degrees C and ATP-independent. Following incubation of JSR with ruthenium red, Ca2+ uptake in the presence or absence of IP4 was further enhanced 2.5 fold. Both basal and IP4-stimulated Ca2+ uptake were half-maximal and maximal in the presence of 60 nM and 180 nM Ca2+, respectively. These studies indicate that IP4 stimulates an ATP-independent Ca2+ uptake mechanism in cardiac JSR which may function to promote rapid Ca2+ loading.
Quist
E E
EE
Department of Pharmacology, University of North Texas Health Science Center at Fort Worth 76107.
Foresman
B H
BH
Vasan
R
R
Quist
C W
CW
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004285:Dogs; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D007295:Inositol Phosphates / Q000494:pharmacology*; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*
D007295:Inositol Phosphates; C081655:inositol-1,3,4,5-tetrakisphosphate; C044259:inositol 1,4-bis(phosphate); D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D002118:Calcium