G-protein modulation of alpha 1A (P/Q) type calcium channel expressed in GH3 cells.

GH3 cell lines stably expressing alpha 1A channel were established and the modulation of this channel by G-protein through membrane-delimited pathways were studied. Wild type GH3 cells were found to express omega-conotoxin MVIIC (MVIIC) sensitive Ca2+ current but this component was different from the alpha 1A channel because of its susceptibility to G-protein modulation, suggesting MVIIC also blocks channels other than P/Q type. Alpha 1A channel expressed in GH3 cells showed slowing of activation and reduction of current amplitude by the application of carbachol. Both of these effects were pertussis toxin (PTX) sensitive and voltage dependent. alpha 1A channels were also found to be modulated through a PTX insensitive pathway, the modulations observed were similar to those in the PTX sensitive pathway. The results further suggest that these two effects are governed by a different mechanism in both PTX sensitive and insensitive pathways.