A GALANIN-MASTOPARAN CHIMERIC PEPTIDE ACTIVATES THE NA-ATPASE AND REVERSES ITS INHIBITION BY OUABAIN(,K+)

The effect of the neuropeptide galanin, the wasp venom toxin amphiphil ic peptide toxin mastoparan and the chimeric peptide, galparan, consis ting of N-terminal 13 amino acids of neuropeptide galanin linked at C- terminus to mastoparan amide (and its inactive analog Mas17) on the ac tivity of Na+,K+-ATPase has been studied. Mastoparan inhibits the acti vity of the Na+,K+-ATPase with IC50 = 7.5 mu M and also reduces the co operativity for Na+ and K+, respectively, while galanin has no effect on the Na+,K+-ATPase activity. The chimeric peptide, galanin(1-13)-mas toparan amide (galparan), exhibits biphasic interaction with Na+,K+-AT Pase, 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 th e cooperativity only for Na+ and it also counteracts the inhibitory ef fect of oubain on Na+,K+-ATPase. Galparan's stimulatory effect was inf luenced by ATP. The chimeric peptide [(19)Lys,(26)Leu]-galparan, conta ining the inactive analog of mastoparan (Mas17), has no effects on rat brain Na+,K+-ATPase activity. Both chimeric peptides galparan and [(1 9)Lys,(26)Leu]-galparan are high-affinity galanin receptor ligands wit h IC50 of 6.4 nM and 0.71 nM, respectively, while galanin (1-13) and m astoparan alone have significantly lower affinity for the galanin rece ptor, IC50 of 125 nM and 1 mu M, respectively. The ability of chimeric peptides to bind to galanin receptors does not correlate with their e ffects on the Na+,K+-ATPase.