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Dimethylsulfoxide modifies the sensitivity of BALB/c‐3T3 cells to the activation of Na+/H+ exchange by phorbol esters

In a companion paper (Gillies et al.: J. Cell. Physiol. 139:124–129, 1989) we show that phorbol esters (PEs) are unable to stimulate Na+/H+ exchange in BALB/C‐3T3 cells under a wide variety of conditions. The Na+/H+ exchangers of a number other cell types are also not responsive to PEs yet have been rendered responsive by treatment with agents such as dimethylsulfoxide (DMSO). We undertook the present study to evaluate whether or not the treatment of BALB/c‐3T3 cells with DMSO will induce modifications in the sensitivity of these cells to activation by PEs. The present study indicates that a 3–5 day exposure of BALB/c‐3T3 cells to 1.25% DMSO leads to changes in the sensitivity of these cells to the activation of Na+/H+ exchanger by PEs. These changes in sensitivity were apparent at day 3 and maximal at day 5. Non‐tumor‐promoting analogues of PEs do not activate Na+/H+ exchange, suggesting that the effect is mediated through kinase C. Sphingosine prevents PE‐, but not serum‐induced alkalinization. However, the half‐time of the intracellular pH (pHin) response to serum was increased by sphingosine, suggesting that kinase C participates in, but is not required for the serum induced activation. Since DMSO does not induce any apparent morphological change, the change in sensitivity of Na+/H+ exchange to PEs is not likely to be related to differentiation, but may be associated with structural changes in the Na+/H+ exchanger and/or changes in isoforms of kinase C which recognize the exchanger as a substrate.