Iodide and bromide inhibit Ca(2+) uptake by cardiac sarcoplasmic reticulum.
Recent studies indicate that the Ca(2+) permeability of the sarcoplasmic reticulum (SR) can be affected by its anionic environment. Additionally, anions could directly modulate the SR Ca(2+) pump or the movement of compensatory charge across the SR membrane during Ca(2+) uptake or release. To examine the effect of anion substitution on cardiac SR Ca(2+) uptake, fluorometric Ca(2+) measurements and spectrophotometric ATPase assays were used. Ca(2+) uptake into SR vesicles was inhibited in a concentration-dependent manner when Br(-) or I(-) replaced extravesicular Cl(-) (when Br(-) completely replaced Cl(-), uptake velocity was approximately 70% of control; when I(-) completely replaced Cl(-), uptake velocity was approximately 39% of control). Replacement of Cl(-) with SO(2)(-4) had no effect on SR uptake. Although both I(-) and Br(-) inhibited net Ca(2+) uptake, neither anion directly inhibited the SR Ca(2+) pump nor did they increase the permeability of the SR membrane to Ca(2+). Our results support the hypothesis that an anionic current that occurs during SR Ca(2+) uptake is reduced by the substitution of Br(-) or I(-) for Cl(-).
Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada T2N 4N1. kargacin@ucalgary.ca
G J
GJ
Kargacin
Z
Z
Ali
S J
SJ
Zhang
N S
NS
Pollock
M E
ME
Kargacin
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001965:Bromides / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D004285:Dogs; D007454:Iodides / Q000494:pharmacology*; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D010070:Oxalates / Q000494:pharmacology; D010539:Permeability; D011189:Potassium Chloride / Q000494:pharmacology; D017680:Potassium Compounds / Q000494:pharmacology; D011193:Potassium Iodide / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019789:Tetraethylammonium / Q000494:pharmacology
D001965:Bromides; D007454:Iodides; D010070:Oxalates; D017680:Potassium Compounds; D009243:NAD; D011193:Potassium Iodide; D019789:Tetraethylammonium; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; C039004:potassium bromide; D002118:Calcium