Volume regulation by flounder red blood cells: the role of the membrane potential.

The nucleated red blood cells of the Winter Flounder Pseudopleuronectes americanus demonstrate a volume regulatory response subsequent to osmotic perturbation. The net water movements associated with response are secondary to net inorganic cation flux. The increased net cation fluxes occur in response to increased cation permeability (Pcation). While ionic strength and cell volume do not appear to be the stimulus for the volume regulatory response i.e. increased Pcation, changes in the cell membrane potential (Vm), as calculated from the chloride distribution ratio, do appear to result in increased Pcation. These studies demonstrate that manipulations leading to membrane hyperpolarization result in net loss of cellular K and water. In contrast treatments which depolarize Vm lead to cellular uptake of Na, K, Cl and water.