Phospholipid subclass-specific alterations in the kinetics of ion transport across biologic membranes.

Abstract

Although the predominance of plasmalogens in electrically-active membranes (e.g., sarcolemma) is well-known, identification of the molecular mechanisms through which the vinyl ether linkage facilitates electrophysiologic function has remained elusive. Herein we demonstrate that the kinetics of both carrier-mediated (i.e., valinomycin) and passive ion transport are substantially different in membranes comprised of plasmalogen molecular species in comparison to their diacyl and alkyl ether choline glycerophospholipid subclass counterparts. The rank order of valinomycin-mediated K+/Na+ exchange in membranes comprised of each choline glycerophospholipid subclass was plasmenylcholine (kappa = (6.1 +/- 0.7) x 10(-2) s-1) > plasmanylcholine (kappa = (1.9 +/- 0.2) x 10(-2) s-1) approximately equal to phosphatidylcholine (kappa = (2.3 +/- 0.5) x 10(-2) s-1). A similar hierarchy of rate constants for valinomycin-facilitated Na+ transport in each subclass was manifest. In contrast, the phospholipid subclass rank order for passive Cl- flux was phosphatidylcholine (kappa = (2.6 +/- 0.4) x 10(-4) s-1) > plasmanylcholine (kappa = (0.8 +/- 0.1) x 10(-4) s-1) approximately equal to plasmenylcholine (kappa = (0.6 +/- 0.2) x 10(-4) s-1). Based upon known differences in the conformation, dynamics, membrane dipole potential, and electron-donating properties of these choline glycerophospholipid subclasses, a model is presented which explains the subclass-induced differences in carrier-mediated and passive ion transport providing a rationale for the predominance of plasmalogens in electrically-active membranes.