MODULATION OF BRAIN NA-PROTEIN-COUPLED PATHWAY( CHANNELS BY A G)

Na+ channels in acutely dissociated rat hippocampal neurons and in Chi nese hamster ovary (CHO) cells transfected with a cDNA encoding the al pha subunit of rat brain type IIA Na+ channel (CNaIIA-1 cells) are mod ulated by guanine nucleotide binding protein (G protein)-coupled pathw ays under conditions of whole cell voltage clamp. Activation of G prot eins by 0.2-0.5 mM guanosine 5'-[gamma-thio]triphosphate (GTP[gamma S] ), a nonhydrolyzable GTP analog, increased Na+ currents recorded in bo th cell types. The increase in current amplitude was caused by an 8- t o 10-mV negative shift in the voltage dependence of both activation an d inactivation. The effects of G-protein activators were blocked by tr eatment with pertussis toxin or guanosine 5'-[gamma-thio]diphosphate ( GDP[gamma]), a nonhydrolyzable GDP analog, but not by cholera toxin. G DP[beta S] (2 mM) alone had effects opposite those of GTP[gamma S], sh ifting Na+-channel gating 8-10 mV toward more-positive membrane potent ials and suggesting that basal activation of G proteins in the absence of stimulation is sufficient to modulate Na+ channels. In CNaIIA-1 ce lls, thrombin, which activates pertussis toxin-sensitive G proteins in CHO cells, caused a further negative shift in the voltage dependence of Na+-channel activation and inactivation beyond that observed with G TP alone. The results in CNaIIA-1 cells indicate that the alpha subuni t of the Na+ channel alone is sufficient to mediate G protein effects on gating. The modulation of Na+ channels via a G-protein-coupled path way acting on Na+-channel alpha subunits may regulate electrical excit ability through integration of different G protein coupled synaptic in puts.