DIFFERENT OMEGA-CONOTOXINS MARK THE DEVELOPMENT OF SWISS WEBSTER MOUSE CORTEX SUGGESTING N-TYPE VOLTAGE-SENSITIVE CALCIUM-CHANNEL SUBTYPES

omega-GVIA conotoxin has been used to mark presynaptic N-type voltage sensitive calcium channels (VSCC).(3,13,19,21-23) Litzinger er al.(9) used omega-conotoxin binding to describe a critical period of neurodev elopment in Swiss Webster mice between postnatal days (PND) 11 and 14, which appears to be important to the initiation of proper final devel opment of the central nervous system. In this study, we compare how th ree different omega-conotoxins (i.e. GVIA from Conus geographus, MVIIA from Conus magus, and RVIA from Conus radiatus) mark N-type VSCC duri ng this critical period in Swiss Webster mouse cortex. I-125-GVIA was bound to Swiss Webster mouse cortex synaptosomal membrane fractions at postnatal days 8 and 14. I-125-GVIA binding displacement curves were obtained by incubating membranes with increasing concentrations of unl abeled GVIA, MVIIA, and RVIA. Displacement curves and IC50 were calcul ated for each of these three omega-conotoxins, and then compared. At P ND 14, GVIA, MVIIA and RVIA were able to displace greater than 95% of I-125-GVIA binding. At PND 8, however, MVIIA was only able to displace 83% of I-125-GVIA binding, and RVIA was only able to block 84%. The I C50 does not appear to change significantly during this period of deve lopment for any of the omega-conotoxins. The inability of MVIIA and RV IA to completely block I-125-GVIA binding in pre-critical period Swiss Webster cortex denotes an alteration in the composition of N-type VSC C binding sites. With this data, we have suggested the presence of sub types of the N-type VSCC in the cortex of pre-critical period Swiss We bster mouse.