GALANTIDE DISTINGUISHES PUTATIVE SUBTYPES OF GALANIN RECEPTORS IN MUDPUPPY PARASYMPATHETIC NEURONS

The effect of the chimeric ligand galantide on the galanin-induced act ivation of membrane K+ conductance and inhibition of voltage-dependent Ca2+ conductance has been studied using voltage-clamped dissociated m udpuppy parasympathetic neurons. Galantide did not activate the K+ con ductance but produced a concentration-dependent antagonism (IC50=4 nM) of the galanin-induced increase in K+ conductance. Galantide acted li ke galanin and inhibited the voltage-dependent Ba2+ current (I-Ba). Th e inhibition of I-Ba also was concentration dependent (IC50=16 nM) and the maximum inhibition produced by galantide was approximately 40%. W e also demonstrate that the galanin-(1-16) fragment increased the memb rane K+ conductance and decreased I-Ba, suggesting that the NH2 portio n of the galanin molecule is sufficient to mediate both actions. One i nterpretation of these observations is that different galanin receptor s mediate the different effects of galanin on the mudpuppy parasympath etic neurons.