Hypotonic swelling-induced Ca(2+) release by an IP(3)-insensitive Ca(2+) store.
Hypotonic swelling increases the intracellular Ca(2+) concentration ([Ca(2+)](i)) in vascular smooth muscle cells (VSMC). The source of this Ca(2+) is not clear. To study the source of increase in [Ca(2+)](i) in response to hypotonic swelling, we measured [Ca(2+)](i) in fura 2-loaded cultured VSMC (A7r5 cells). Hypotonic swelling produced a 40.7-nM increase in [Ca(2+)](i) that was not inhibited by EGTA but was inhibited by 1 microM thapsigargin. Prior depletion of inositol 1,4,5-trisphosphate (IP(3))-sensitive Ca(2+) stores with vasopressin did not inhibit the increase in [Ca(2+)](i) in response to hypotonic swelling. Exposure of (45)Ca(2+)-loaded intracellular stores to hypotonic swelling in permeabilized VSMC produced an increase in (45)Ca(2+) efflux, which was inhibited by 1 microM thapsigargin but not by 50 microg/ml heparin, 50 microM ruthenium red, or 25 microM thio-NADP. Thus hypotonic swelling of VSMC causes a release of Ca(2+) from the intracellular stores from a novel site distinct from the IP(3)-, ryanodine-, and nicotinic acid adenine dinucleotide phosphate-sensitive stores.
Mohanty
M J
MJ
Department of Medicine, Wayne State University School of Medicine and John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan 48201, USA. jenam@intmed.wayne.edu
Ye
M
M
Li
X
X
Rossi
N F
NF
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007038:Hypotonic Solutions / Q000494:pharmacology*; D015544:Inositol 1,4,5-Trisphosphate / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D009249:NADP / Q000031:analogs & derivatives / Q000494:pharmacology; D009994:Osmolar Concentration; D012433:Ryanodine / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology
D004791:Enzyme Inhibitors; D007038:Hypotonic Solutions; D012433:Ryanodine; D009249:NADP; C024376:NAADP; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium