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Marine Biological Laboratory, Woods Hole, MA 02543

Correspondence to R.F. Rakowski: rakowski{at}ohio.edu; or D.C. Gadsby: gadsby{at}rockefeller.edu

Palytoxin binds to Na⁺/K⁺ pumps in the plasma membrane of animal cells and opens an electrodiffusive cation pathway through the pumps. We investigated properties of the palytoxin-opened channels by recording macroscopic and microscopic currents in cell bodies of neurons from the giant fiber lobe, and by simultaneously measuring net current and ²²Na⁺ efflux in voltage-clamped, internally dialyzed giant axons of the squid Loligo pealei. The conductance of single palytoxin-bound "pump-channels" in outside-out patches was 7 pS in symmetrical 500 mM [Na⁺], comparable to findings in other cells. In these high-[Na⁺], K⁺-free solutions, with 5 mM cytoplasmic [ATP], the K_0.5 for palytoxin action was 70 pM. The pump-channels were 40–50 times less permeable to N-methyl-D-glucamine (NMG⁺) than to Na⁺. The reversal potential of palytoxin-elicited current under biionic conditions, with the same concentration of a different permeant cation on each side of the membrane, was independent of the concentration of those ions over the range 55–550 mM. In giant axons, the Ussing flux ratio exponent (n') for Na⁺ movements through palytoxin-bound pump-channels, over a 100–400 mM range of external [Na⁺] and 0 to –40 mV range of membrane potentials, averaged 1.05 ± 0.02 (n = 28). These findings are consistent with occupancy of palytoxin-bound Na⁺/K⁺ pump-channels either by a single Na⁺ ion or by two Na⁺ ions as might be anticipated from other work; idiosyncratic constraints are needed if the two Na⁺ ions occupy a single-file pore, but not if they occupy side-by-side binding sites, as observed in related structures, and if only one of the sites is readily accessible from both sides of the membrane.

P. Artigas' and D.C. Gadsby's address is Laboratory of Cardiac/Membrane Physiology, Rockefeller University, 1230 York Avenue, New York, NY 10021.

F. Palma's and M. Holmgren's address is National Institutes of Health, NINDS, Bethesda, MD 20892.

P. De Weer's address is Department of Physiology, University of Pennsylvania, School of Medicine, 3700 Hamilton Walk, Philadelphia, PA 19104.

Abbreviations used in this paper: NMG⁺, N-methyl-D-glucamine; PPTEA, phenylpropyltriethylammonium.

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				D. C Gadsby, A. Takeuchi, P. Artigas, and N. Reyes Peering into an ATPase ion pump with single-channel recordings Phil Trans R Soc B, January 27, 2009; 364(1514): 229 - 238. [Abstract] [Full Text] [PDF]

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