Cell type-specific modes of feedback regulation of capacitative calcium entry.
The Ca2+-ATPase inhibitor, thapsigargin, activated Ca2+ entry into pancreatic acinar cells, a process known as capacitative calcium entry. In cells loaded with the calcium chelator BAPTA, the transient Ca2+ release was blunted and the rise of [Ca2+]i on readdition of Ca2+ was slowed. However, the steady-state [Ca2+]i due to Ca2+ entry was substantially augmented compared with control cells. This indicates that [Ca2+]i exerts a negative feedback on Ca2+ entry from a compartment buffered by BAPTA and separated from the bulk of cytoplasmic Ca2+. This interaction probably occurs close to the calcium channel where [Ca2+] is higher than in the bulk of the cytoplasm. In support of this interpretation, the slower Ca2+ chelator, EGTA, also blunted the release of Ca2+ and slowed the rise of the sustained [Ca2+]i phase but failed to augment steady-state [Ca2+]i. In contrast, Ca2+ entry in NIH 3T3 cells was characterized by a transient rise of [Ca2+]i that decays to near prestimulus levels. This decay in Ca2+ entry also results from negative feedback by Ca2+ because the decrease in Ca2+ entry was reversed by incubation in a Ca2+-deficient medium. However, unlike its effects in acinar cells, BAPTA neither augmented steady-state [Ca2+]i nor prevented the inactivation of entry. Rather, in BAPTA-loaded cells, [Ca2+]i failed to increase substantially suggesting that negative regulation by Ca2+ may occur at a site distinct from the cytoplasmic compartment and inaccessible to cytoplasmic BAPTA. These two distinct types of feedback behavior may indicate subtypes of store-operated calcium channels expressed in different cells or a single type of channel which is differentially regulated in a cell type-specific manner.
Louzao
M C
MC
Calcium Regulation Section, Laboratory of Cellular and Molecular Pharmacology, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
Ribeiro
C M
CM
Bird
G S
GS
Putney
J W
JW
D016475:3T3 Cells; D000704:Analysis of Variance; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005246:Feedback; D005456:Fluorescent Dyes; D016257:Fura-2; D007700:Kinetics; D051379:Mice; D010179:Pancreas / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin; D013997:Time Factors
D002614:Chelating Agents; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D013729:Terpenes; D004533:Egtazic Acid; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium; D016257:Fura-2