Sugar transport in giant barnacle muscle fibres.

Abstract

The kinetics of 3-O-methylglucose transport in the giant muscle cells of B. nubilus were studied in intact fibers and in fibers subjected to intracellular solute control using internal dialysis. 3-O-methylglucose is not metabolized by barnacle muscle and at equilibrium the 3-O-methylglucose space of the tissue does not differ significantly from the water content of the muscle. 3-O-methylglucose transfer in barnacle muscle probably is mediated by a passive process. 3-O-methylglucose transport is facilitated by a saturable, symmetric transfer mechanism inhibited by cis but not trans sugars and by low concentrations of phloretin and cytochalasin B. The kinetic constants for uptake and exit are identical. Sugar transport in barnacle muscle probably is mediated by a limited number of membrane transport sites. The number of sugar-displaceable cytochalasin B binding sites in barnacle muscle is 3 .times. 1013 cm-2. Indirect kinetic estimates indicate that the number of sugar transport sites is in the order of 1.6 .times. 1012 cm-2. This passive, facilitated, selective, saturable transport system is consistent with both symmetric mobile carrier (1-site) and symmetric simultaneous carrier (2-site) models for transport.