RELATIONSHIP BETWEEN SPECIFIC BINDING OF I-125 OMEGA-CONOTOXIN GVIA AND GTP-BINDING PROTEIN - EFFECTS OF THE GTP ANALOGS, MASTOPARAN AND ALF4-

We investigated whether the specific binding or labeling of I-125-omeg a-CgTX on crude membranes from chick whole brain was affected when end ogenous GTP binding protein (G protein) was activated by GTP analogues , mastoparan (MP) and aluminum fluoride (AlF4-; AlCl3 + NaF). Both GTP gamma S and Gpp(NH)p attenuated the inhibitory effect of selective N- type Ca channel inhibitors such as aminoglycoside antibiotics (AGs) or dynorphine (l-13)(Dyn) on specific I-125-omega-CgTX binding in a dose -dependent manner. On the other hand, the inhibitory effects of the di valent metal cations Cd2+, Co2+, Mg2+ and Mn2+ on such binding were no t attenuated by GTP gamma S. MP and AlF4- also attenuated the inhibito ry effect of Neo on this binding similar to GTP gamma S. The attenuati ng effect of MP was enhanced by the presence of Mg2+ in a dose-depende nt manner. However, GTP analogues, MP and AlF4-, did not affect bindin g or labeling without AGs or Dyn. GTP gamma S, MP and AlF4- also atten uated the specific labeling of a 215-kDa band in crude membranes with I-125-omega-CgTX using the cross-linker DSS (non-reduced condition) in the presence of Neo. These results indicate that there are direct or indirect relationships between N-type Ca channels and G proteins via b inding sites for AGs or MP.