Differences in uptake, storage and release properties between inositol trisphosphate-sensitive and -insensitive Ca2+ stores in permeabilized pancreatic acinar cells.
Rabbit pancreatic acinar cells, permeabilized by saponin treatment, were used to study the kinetics of ATP-dependent Ca2+ uptake and release in inositol 1,4,5-trisphosphate (Ins-1,4,5-P3)-sensitive and -insensitive stores. Permeabilized acinar cells rapidly accumulated Ca2+ to steady-state. At steady state, approximately 60% of actively stored Ca2+ resided in the Ins-1,4,5-P3-sensitive store. Kinetic analysis of the Ca2+ uptake process revealed that the initial Ca2+ uptake rate was 1.7 times higher in the Ins-1,4,5-P3-insensitive store as compared to the Ins-1,4,5-P3-sensitive store. On the other hand, the Ca2+ uptake capacity was 1.6 times higher in the Ins-1,4,5-P3-sensitive store as compared to the Ins-1,4,5-P3-insensitive store. The Ca2+ uptake rate in the Ins-1,4,5-P3-sensitive store remained virtually constant for at least 4 min, whereas in the Ins-1,4,5-P3-insensitive Ca2+ store this rate progressively declined with time. These observations are compatible with: (i) an Ins-1,4,5-P3-sensitive store containing relatively few Ca2+ pumps but possessing a relatively high Ca2+ uptake capacity, which may reflect the presence of a substantial amount of Ca2+ binding protein; and (ii) an Ins-1,4,5-P3-insensitive Ca2+ store containing relatively many Ca2+ pumps but possessing a relatively low Ca2+ uptake capacity, which may reflect the presence of little if any Ca2+ binding protein. The data presented are consistent with the idea of a heterogeneous distribution of Ca2+ pumps, Ca2+ binding proteins and Ca2+ release channels between intracellular Ca2+ storage organelles.
Van de Put
F H
FH
Department of Biochemistry, University of Nijmegen, The Netherlands.
Nàgy
P
P
De Pont
J J
JJ
Willems
P H
PH
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002451:Cell Compartmentation; D002463:Cell Membrane Permeability; D002469:Cell Separation; D006493:Heparin / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D016623:Ion Pumps / Q000378:metabolism; D015388:Organelles / Q000378:metabolism; D010179:Pancreas / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011817:Rabbits
D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D016623:Ion Pumps; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D006493:Heparin; D002118:Calcium