Actions of mercurials on cell volume regulation of dissociated MDCK cells

The mercurial, p-chloromercuribenzoylsulfonate (PCMBS), blocks volume recovery of dissociated, osmotically swollen, Madin-Darby canine kidney cells (MDCK) and, at higher concentrations, induces substantial swelling. In the absence of Na+ the rate of volume recovery is, in contrast, substantially increased. PCMBS does not inhibit the "normal" volume-regulating pathways, K+ and Cl- conductances. Rather, its blocking action is due to substantial activation of Na+ and K+ permeabilities, especially the former. Consequently, the normal reshrinking mechanism, loss of KCl, is counterbalanced by PCMBS-induced gains of NaCl. In isotonic cells, PCMBS, at higher concentrations, induces cell swelling, indicating that Cl- permeability is also increased, a conclusion confirmed by direct measurement of 36Cl- fluxes. HgCl2 produces similar effects except that it is more potent and more rapid in its action. Activation of conductive ion permeabilities to Na+, K+, and Cl- are associated with appropriate changes in membrane potential. A small bumetanide-sensitive swelling component (Na(+)-Cl- cotransport) is activated by HgCl2 but not by PCMBS. Another effect is elevation of cytoplasmic Ca2+, apparently by mobilization from internal stores. Some of the functional sites (Na+ and K+) appear to be located externally, rapidly accessible to both HgCl2 and PCMBS, whereas others (Cl- and Ca2+) appear to be internal, rapidly accessible to the permeant HgCl2 but slowly to relatively impermeant PCMBS. In conclusion, the disturbances of volume regulation are largely due to the increases in conductive ion fluxes.