Evidence of calcium influx across the plasma membrane depends upon the initial rise of cytosolic calcium with activation of IP3 in rat enterocytes byheat-stable enterotoxin of Vibrio cholerae non-O1

In response to heat-stable enterotoxin of Vibrio cholerae non-O1, the initi al rise of cytosolic Ca2+ occurred with activation of IP3. Chelation of ext racellular Ca2+ with EGTA and suspension of cells in Ca2+ free buffer both demonstrated the involvement of internal stores in the rise of [Ca2+]i. Cel ls pretreated with dantrolene resulted in decrease of [Ca2+]i response whic h suggested that the rise of intracellular level of Ca2+ was mostly due to the mobilization from IP3 sensitive stores. When the cytosolic Ca2+ was che lated by loading the cells with BAPTA, NAG-ST could not induce Ca2+ entry t o the cell as assessed by Mn2+ quenching of fura-2 fluorescence which sugge sted that calcium influx across the plasma membrane depends upon initial ri se of this bivalent cation that maintained the sustained phase of [Ca2+]i r esponse. Addition of toxin to the fura-2-loaded cells, preincubated with la nthanum chloride, resulted in reduction of [Ca2+]i level with a short durat ion of irregular sustained phase further suggesting that the influx of Ca2 across the plasma membrane might be through the calcium channel. (C) 2001 Federation of European Microbiological Societies. Published by Elsevier Sci ence B.V. All rights reserved.