Calcium influx mediated by the Escherichia coli heat-stable enterotoxin B (STB).
The heat-stable enterotoxin B (STB) of Escherichia coli is a 48-amino acid extracellular peptide that induces rapid fluid accumulation in animal intestinal models. Unlike other E. coli enterotoxins that elicit cAMP or cGMP responses in the gut [heat-labile toxin (LT) and heat-stable toxin A (STA), respectively], STB induces fluid loss by an undefined mechanism that is independent of cyclic nucleotide elevation. Here we studied the effects of STB on intracellular calcium concentration ([Ca2+]i), another known mediator of intestinal ion and fluid movement. Ca2+ and pH measurements were performed on different cell types including Madin-Darby canine kidney (MDCK), HT-29/C1 intestinal epithelial cells, and primary rat pituitary cells. Ca2+ and pH determinations were performed by simultaneous real-time fluorescence imaging at four emission wavelengths. This allowed dual imaging of the Ca(2+)- and pH-specific ratio dyes (indo-1 and SNARF-1, respectively). STB treatment induced a dose-dependent increase in [Ca2+]i with virtually no effect on internal pH in all of the cell types tested. STB-mediated [Ca2+]i elevation was not inhibited by drugs that block voltage-gated Ca2+ channels including nitrendipine, verapamil (L-type), omega-conotoxin (N-type), and Ni2+ (T-type). The increase in [Ca2+]i was dependent on a source of extracellular Ca2+ and was not affected by prior treatment of MDCK cells with thapsigargin or cyclopiazonic acid, agents that deplete and block internal Ca2+ stores. In contrast to these results, somatostatin and pertussis toxin pretreatment of MDCK cells completely blocked the STB-induced increase in [Ca2+]i. Taken together, these data suggest that STB opens a GTP-binding regulatory protein-linked receptor-operated Ca2+ channel in the plasma membrane. The nature of the STB-sensitive Ca2+ channel is presently under investigation.
Dreyfus
L A
LA
Division of Cell Biology, University of Missouri, Kansas City 64110-2499.
Harville
B
B
Howard
D E
DE
Shaban
R
R
Beatty
D M
DM
Morris
S J
SJ
D000818:Animals; D001427:Bacterial Toxins / Q000302:isolation & purification / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002460:Cell Line; D002478:Cells, Cultured; D004285:Dogs; D004768:Enterotoxins / Q000302:isolation & purification / Q000494:pharmacology*; D004926:Escherichia coli; D029968:Escherichia coli Proteins; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D007668:Kidney; D007700:Kinetics; D008297:Male; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013050:Spectrometry, Fluorescence; D013997:Time Factors
D001427:Bacterial Toxins; D002121:Calcium Channel Blockers; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D005456:Fluorescent Dyes; C034151:heat stable toxin (E coli); D002118:Calcium