Cost, effectiveness and environmental relevance of multidrug transporters in sea urchin embryos

Citation:
Cole, BJ, Hamdoun A, Epel D.  2013.  Cost, effectiveness and environmental relevance of multidrug transporters in sea urchin embryos. Journal of Experimental Biology. 216:3896-3905.

Date Published:

10/2013

Keywords:

abc, ABC transporters, environmental toxicology, P-GP, MRP, Strongylocentrotus purpuratus, activity, blood-brain-barrier, drug transport, efflux transporters, keler v, 1995, biochemical and biophysical research communications, v208, p345, na+/k+-atpase, oatp transporters, p-glycoprotein reveals, strongylocentrotus-purpuratus, transmembrane movement, transporters, trout oncorhynchus-mykiss

Abstract:

ATP-binding cassette transporters protect cells via efflux of xenobiotics and endogenous byproducts of detoxification. While the cost of this ATP-dependent extrusion is known at the molecular level, i.e. the ATP used for each efflux event, the overall cost to a cell or organism of operating this defense is unclear, especially as the cost of efflux changes depending on environmental conditions. During prolonged exposure to xenobiotics, multidrug transporter activity could be costly and ineffective because effluxed substrate molecules are not modified in the process and could thus undergo repeated cycles of efflux and re-entry. Here we use embryos of the purple sea urchin, Strongylocentrotus purpuratus, as a model to determine transport costs and benefits under environmentally relevant xenobiotic concentrations. Strikingly, our results show that efflux transporter activity costs less than 0.2% of total ATP usage, as a proportion of oxygen consumption. The benefits of transport, defined as the reduction in substrate accumulation due to transporter activity, depended largely, but not entirely, on the rate of passive flux of each substrate across the plasma membrane. One of the substrates tested exhibited rapid membrane permeation coupled with high rates of efflux, thus inducing rapid and futile cycles of efflux followed by re-entry of the substrate. This combination significantly reduced transporter effectiveness as a defense and increased costs even at relatively low substrate concentrations. Despite these effects with certain substrates, our results show that efflux transporters are a remarkably effective and low-cost first line of defense against exposure to environmentally relevant concentrations of xenobiotics.

Notes:

n/a

Website

DOI:

10.1242/jeb.090522