Calcium ionophore (A23187) was obtained from Calbiochem. BAPTA-AM [1,2-bis(o-aminophenoxy)ethane-N,N,N8,N8-tetraacetic acid tetra-(acetoxymethyl) ester] and 1/2 BAPTA-AM were obtained from Molecular Probes. Parasites (4´107 mlÿ1) were exposed to 20mM BAPTA-AM or 1/2 BAPTAAM at 188C for 20min, followed by one wash in Hanks' balanced salt solution (HBSS; Gibco BRL) and resuspension at 4´107 mlÿ1 in invasion medium with or without 25mM A23187. After incubation for 15min at 378C, supernatants were harvested for analysis by Western blot to detect MIC2