Apparent receptor-mediated activation of Ca -dependent conductive Cl transport by shark-derived polyaminosterols

Chernova, Marina N., David H. Vandorpe, Jeffrey S. Clark, Jon I. Williams, Michael A. Zasloff, Lianwei Jiang, and Seth L. Alper. Apparent receptor-mediated activation of Ca -dependent conductive Cl transport by shark-derived polyaminosterols. Am J Physiol Regul Integr Comp Physiol 289: R1644–R1658, 2005. First published August 18, 2005; doi:10.1152/ajpregu.00098.2005.—The shark liver antimicrobial polyaminosterol squalamine is an angiogenesis inhibitor under clinical investigation as an anti-cancer agent and as a treatment for the choroidal neovascularization associated with macular degeneration of the retina. The related polyaminosterol MSI1436 is an appetite suppressant that decreases systemic insulin resistance. However, the mechanisms of action of these polyaminosterols are unknown. We report effects of MSI-1436 on Xenopus oocytes consistent with the existence of a receptor for polyaminosterols. MSI-1436 activates bidirectional, trans-chloride-independent Cl flux in Xenopus oocytes. At least part of this DIDS-sensitive Cl flux is conductive, as measured using two-electrode voltage-clamp and oncell patch-clamp techniques. MSI-1436 also elevates cytosolic Ca concentration ([Ca ]) and increases bidirectional Ca flux. Activation of Cl flux and elevation of cytosolic [Ca ] by MSI-1436 both are accelerated by lowering bath Ca and are not acutely inhibited by extracellular EGTA. Elevation of cytosolic [Ca ] by MSI-1436 requires heparin-sensitive intracellular Ca stores. Although injected EGTA abolishes the increased conductive Cl flux, that Cl flux is not dependent on heparin-sensitive stores. In low-bath Ca conditions, several structurally related polyaminosterols act as strong agonists or weak agonists of conductive Cl flux in oocytes. Weak agonist polyaminosterols antagonize the strong agonist, MSI1436, but upon addition of the conductive Cl transport inhibitor DIDS, they are converted into strong agonists. Together, these properties operationally define a polyaminosterol receptor at or near the surface of the Xenopus oocyte, provide an initial description of receptor signaling, and suggest routes toward further understanding of a novel class of appetite suppressants and angiogenesis inhibitors.