Alteration in Ca2+ homeostasis by a trauma peptide.
Postinjury tissue inflammation with PMN elastase proteolysis generates immunosuppressive fibronectin peptides (FNDP) impairing chemotaxis, T-cell activation, and proliferation. Excess intracellular Ca2+ ([Ca2+]i) impairs T-cell activation. This study quantifies the changes in [Ca2+]i following exposure to a degradation peptide of fibronectin to determine the mechanism of action of these peptides on calcium homeostasis. Isolated human PBLs were exposed to immunosuppressive concentrations of FNDP after loading with the [Ca2+]i probe FURA-2AM. Resting and sustained [Ca2+]i concentrations were calculated and compared to buffer control. The mechanism of action was determined by pretreatment with: (1) EDTA binding extra cellular Ca2+: [Ca2+]e, (2) the Ca2+ channel blockers verapamil and nifedipine, and (3) inhibition of [Ca2+]i released by dantrolene. Inositol triphosphate (IP3) essential for [Ca2+]i release was measured following T-cell stimulation as well. FNDP caused 200-400% increases in [Ca2+]i concentration relative to buffer control at known suppressive doses. Verapamil and nifedipine partially block [Ca2+]i influx by as much as 50% suggesting the slow Ca2+ (voltage independent) channels are partially responsible for the increased [Ca2+]i seen following FNDP. EDTA completely suppressed [Ca2+]e influx but did not completely inhibit the release of [Ca2+]i although IP3 was 80% suppressed. The increase in [Ca2+]i following FNDP stimulation is due to release of intracellular stores.
Hoyt
D B
DB
Department of Surgery, University of California, San Diego 92103.
Ozkan
A N
AN
Frevert
J
J
Junger
W G
WG
Loomis
W H
WH
D002118:Calcium / Q000097:blood*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D003620:Dantrolene / Q000494:pharmacology; D005353:Fibronectins / Q000494:pharmacology*; D006020:Glycopeptides; D006706:Homeostasis; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D009000:Monocytes / Q000378:metabolism; D009543:Nifedipine / Q000494:pharmacology; D011458:Prostaglandins E; D014700:Verapamil / Q000494:pharmacology; D014947:Wounds and Injuries / Q000097:blood*
D002121:Calcium Channel Blockers; D005353:Fibronectins; D006020:Glycopeptides; D007295:Inositol Phosphates; D011458:Prostaglandins E; C045872:suppressor active peptide (thermal injury); D014700:Verapamil; D003620:Dantrolene; D009543:Nifedipine; D002118:Calcium