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

Abstract

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 IC 50 = 7.5 μM 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 μM followed by inhibition of the enzyme with IC 50 of 100 μM. At maximum stimulating concentration (4 μM), 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 [ 19Lys, 26Leu]-galparan, containing the inactive analog of mastoparan (Mas17), has no effects on rat brain Na +,K +-ATPase activity. Both chimeric peptides galparan and [ 19Lys, 26Leu]-galparan are high-affinity galanin receptor ligands with IC 50 of 6.4 nM and 0.71 nM, respectively, while galanin (1–13) and mastoparan alone have significantly lower affinity for the galanin receptor, IC 50 of 125 nM and 1 μM, respectively. The ability of chimeric peptides to bind to galanin receptors does not correlate with their effects on the Na +,K +-ATPase.