A galanin-mastoparan chimeric peptide activates the Na+,K+-ATPase and reverses its inhibition by ouabain

The effect of the neuropeptide galanin, the wasp venom toxin amphiphilic peptide toxin mastoparan and the chimeric peptide, galparan, consisting of N-terminal 13 amino acids of neuropeptide galanin linked at C-terminus to mastoparan amide (and its inactive analog Mas17) on the activity of Na+,K+-ATPase has been studied. Mastoparan inhibits the activity of the Na+,K+-ATPase with IC50 = 7.5 mu M and also reduces the cooperativity for Na+ and K+, respectively, while galanin has no effect on the Na+,K+-ATPase activity. The chimeric peptide, galanin(1-13)-mastoparan amide (galparan), exhibits biphasic interaction with Na+,K+-ATPase, it activates the enzyme at maximal stimulating concentration of 4 mu M followed by inhibition of the enzyme with IC50 of 100 mu M. At maximum stimulating concentration (4 mu M), galparan partly reduces the cooperativity only for Na+ and it also counteracts the inhibitory effect of oubain on Na+,K+-ATPase. Galparan's stimulatory effect was influenced by ATP. The chimeric peptide [(19)Lys,(26)Leu]-galparan, containing the inactive analog of mastoparan (Mas17), has no effects on rat brain Na+,K+-ATPase activity. Both chimeric peptides galparan and [(19)Lys,(26)Leu]-galparan are high-affinity galanin receptor ligands with IC50 of 6.4 nM and 0.71 nM, respectively, while galanin (1-13) and mastoparan alone have significantly lower affinity for the galanin receptor, IC50 of 125 nM and 1 mu M, respectively. The ability of chimeric peptides to bind to galanin receptors does not correlate with their effects on the Na+,K+-ATPase.