Characterization of calcium involvement in the Clostridium perfringens type A enterotoxin-induced release of 3H-nucleotides from Vero cells.

This report characterizes the involvement of Ca2+ in the release of nucleotides from Vero cells caused by Clostridium perfringens enterotoxin (CPE). A positive linear correlation was observed between increased CPE-induced nucleotide-release and increased extracellular calcium over the range 0.01 to 10 mM calcium. Above 5 mM Ca2+, CPE-specific lysis (i.e. disintegration of cells as monitored by light microscopy) was observed. Addition of 1.7 mM Ca2+ to Vero cells previously CPE-treated in Ca2+-free buffer rapidly increased nucleotide-release, even when cells had been previously incubated for 1 h at 37 degrees C in Ca2+-free buffer. Withdrawal of Ca2+, even after the onset of nucleotide-release, halted further CPE-induced nucleotide-release. These results indicate that Ca2+ must be continuously present for significant CPE-induced nucleotide-release. However, withdrawal of Ca2+ did not reverse membrane bleb formation by CPE. This differentiates bleb formation and nucleotide-release (both Ca2+-dependent CPE effects) and suggests that nucleotide-release does not result simply from bleb formation. Lastly, it was shown that other ions besides physiologic Ca2+ (1.7 mM) are required for CPE-induced nucleotide-release. Interestingly, a role for other ions (but not physiologic Ca2+) is also shown for 86Rb-release by CPE (an early Ca2+-independent CPE effect). This indicates that extracellular ions other than physiologic Ca2+ can be required for both Ca2+-independent and Ca2+-dependent CPE effects.