Syed R. Akhter

Exogenous calmodulin potentiates vasodilation elicited by phospholipid-associated VIP in vivo.

The purpose of this study was to determine whether exogenous calmodulin potentiates vasoactive intestinal peptide (VIP)-induced vasodilation in vivo and, if so, whether this response is amplified by association of VIP with sterically stabilized liposomes. Using intravital microscopy, we found that calmodulin suffused together with aqueous and liposomal VIP did not potentiate vasodilation elicited by VIP in the in situ hamster cheek pouch. However, preincubation of calmodulin with liposomal, but not aqueous, VIP for 1 and 2 h and overnight at 4°C before suffusion significantly potentiated vasodilation ( P < 0.05). Calmodulin-induced responses were significantly attenuated by calmidazolium, trifluoperazine, and N G-nitro-l-arginine methyl ester (l-NAME) but notd-NAME. The effects ofl-NAME were reversed byl- but notd-arginine. Indomethacin had no significant effects on calmodulin-induced responses. Calmodulin had no significant effects on adenosine-, isoproterenol-, acetylcholine-, and calcium ionophore A-23187-induced vasodilation. Collectively, these data indicate that exogenous calmodulin amplifies vasodilation elicited by phospholipid-associated, but not aqueous, VIP in the in situ peripheral microcirculation in a specific, calmodulin active sites-, and nitric oxide-dependent fashion. We suggest that extracellular calmodulin, phospholipids, and VIP form a novel functionally coordinated class of endogenous vasodilators.The purpose of this study was to determine whether exogenous calmodulin potentiates vasoactive intestinal peptide (VIP)-induced vasodilation in vivo and, if so, whether this response is amplified by association of VIP with sterically stabilized liposomes. Using intravital microscopy, we found that calmodulin suffused together with aqueous and liposomal VIP did not potentiate vasodilation elicited by VIP in the in situ hamster cheek pouch. However, preincubation of calmodulin with liposomal, but not aqueous, VIP for 1 and 2 h and overnight at 4 degrees C before suffusion significantly potentiated vasodilation (P < 0.05). Calmodulin-induced responses were significantly attenuated by calmidazolium, trifluoperazine, and NG-nitro-L-arginine methyl ester (L-NAME) but not D-NAME. The effects of L-NAME were reversed by L- but not D-arginine. Indomethacin had no significant effects on calmodulin-induced responses. Calmodulin had no significant effects on adenosine-, isoproterenol-, acetylcholine-, and calcium ionophore A-23187-induced vasodilation. Collectively, these data indicate that exogenous calmodulin amplifies vasodilation elicited by phospholipid-associated, but not aqueous, VIP in the in situ peripheral microcirculation in a specific, calmodulin active sites-, and nitric oxide-dependent fashion. We suggest that extracellular calmodulin, phospholipids, and VIP form a novel functionally coordinated class of endogenous vasodilators.

Human galanin expresses amphipathic properties that modulate its vasoreactivity in vivo

The purpose of this study was to determine whether human galanin, a pleiotropic 30-amino acid neuropeptide, expresses amphipathic properties in vitro and, if so, whether these properties modulate its vasoactive effects in the intact peripheral microcirculation. We found that human galanin aggregates in an aqueous solution and forms micelles with a critical micellar concentration (CMC) of 0.4 microM. In addition, the peptide interacted with model membrane as indicated by long and significant increase of the surface pressure of the biomimetic monolayer membrane in vitro. Interactions of human galanin with sterically stabilized phospholipid micelles (SMM) were not associated with a significant change in peptide conformation. Using intravital microscopy, we found that suffusion of human galanin alone elicited significant concentration-dependent vasoconstriction in the intact hamster cheek pouch. This response was amplified when human galanin in SSM was suffused onto the cheek pouch. The effects of human galanin alone and in SSM were mediated by galanin receptors because galantide, a galanin receptor antagonist, abrogated galanin-induced vasoconstriction. Collectively, these data show that human galanin expresses amphipathic properties in the presence of phospholipids which in turn amplifies its vasoactive effects in the intact peripheral microcirculation.