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

Abstract

In response to heat-stable enterotoxin of Vibrio cholerae non-O1, the initial rise of cytosolic Ca²⁺ occurred with activation of IP₃. Chelation of extracellular Ca²⁺ with EGTA and suspension of cells in Ca²⁺ free buffer both demonstrated the involvement of internal stores in the rise of [Ca²⁺]i. Cells pretreated with dantrolene resulted in decrease of [Ca²⁺]i response which suggested that the rise of intracellular level of Ca²⁺ was mostly due to the mobilization from IP₃ sensitive stores. When the cytosolic Ca²⁺ was chelated by loading the cells with BAPTA, NAG-ST could not induce Ca²⁺ entry to the cell as assessed by Mn²⁺ quenching of fura-2 fluorescence which suggested that calcium influx across the plasma membrane depends upon initial rise of this bivalent cation that maintained the sustained phase of [Ca²⁺]i response. Addition of toxin to the fura-2-loaded cells, preincubated with lanthanum chloride, resulted in reduction of [Ca²⁺]i level with a short duration of irregular sustained phase further suggesting that the influx of Ca²⁺ across the plasma membrane might be through the calcium channel.