Responses of lymphocytes to anisotonic media: Volume-regulating behavior

responses elicited in lymphoid cells suspended in anisotonic media are reviewed. The immediate response approximates osmometric behavior. In addition, in hypotonic media, the initial osmometric swelling is followed by a regulatory volume decrease (RVD), which is associated with KC1 loss. The volume-induced effluxes of K ’ and Cl- are mediated by two independ-ent conductive pathways. Ca2+-depletion experiments and studies of inhib-itor susceptibility suggest that Ca2 ’ may mediate the activation of the K’ pathway. The responses of the two main lymphocyte subpopulations to hypotonic challenge are different. RVD is much more rapid in T- than in B-cells, regardless of their tissue of origin Under certain conditions, shrunken lymphocytes will regain their initial volume. This regulatory volume increase (RVI) is due to NaCl uptake, followed by a secondary exchange of Na ’ for K+ via the Na+-K+ pump. Na+ is primarily taken up in exchange for H ’ through an amiloride-sensitive pathway, whereas Cl-enters in exchange for HCOi (or OH-). Anion and cation fluxes responsibl