Behaviour of cardiac microsomal Ca2+ pump under conditions that may simulate pathological situations.
The behaviour of Ca2+ ATPase activity in relation to Ca2+ transport process was studied under different experimental conditions in canine cardiac microsomal fraction predominantly containing sarcoplasmic reticulum. The total Ca2+ concentration required for half maximal activation (Ka) of microsomal Ca2+ ATPase and Ca2+ uptake did not differ significantly, unless 0.1 mmol/l EGTA was present in the incubation media. Pretreatment of cardiac microsomes with membrane disruptive agents like phospholipase A, trypsin as well as deoxycholate strongly increased (2-3 fold) Ca2+ ATPase activity but uptake rate of Ca2+ declined. Only in phospholipase C and beta-glucuronidase pretreatment, a parallel decrease of Ca2+ ATPase and uptake was observed. In presence of excess (free)Ca2+ (greater than 10 mumol/l) both Ca2+ ATPase as well as Ca2+ uptake were inhibited, however, Ca2+ binding process remained unaltered. Likewise, low pH completely altered the relation between Ca2+ binding and ATPase activity; whereas Ca2+ ATPase was inhibited, Ca2+ binding did not change. Our present data provide evidence for some cellular factors that may be involved in producing uncoupling of microsomal Ca2+ ATPase from Ca2+ accumulation process that was previously observed in various pathological situations.
Dhalla
N S
NS
Sulakhe
P V
PV
Lamers
J M
JM
Ganguly
P K
PK
Elimban
V
V
D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D003840:Deoxycholic Acid / Q000494:pharmacology; D004285:Dogs; D005966:Glucuronidase / Q000494:pharmacology; D008861:Microsomes / Q000187:drug effects / Q000201:enzymology; D009206:Myocardium / Q000378:metabolism*; D010741:Phospholipases A / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D014357:Trypsin / Q000494:pharmacology; D010738:Type C Phospholipases / Q000494:pharmacology
D003840:Deoxycholic Acid; D010741:Phospholipases A; D010738:Type C Phospholipases; D005966:Glucuronidase; D014357:Trypsin; D000252:Calcium-Transporting ATPases; D002118:Calcium