TRANSFORMATION OF RENAL TUBULE EPITHELIAL-CELLS BY SIMIAN VIRUS-40 IS ASSOCIATED WITH EMERGENCE OF CA-2+-INSENSITIVE K+ CHANNELS AND ALTERED MITOGENIC SENSITIVITY TO K+ CHANNEL BLOCKERS

We compared the pattern of K+ channels and the mitogenic sensitivity to K+ channel blocking agents in primary cultures of rabbit proximal tubule cells (PC.RC) (Ronco et al., 1990) and two derived SV-40-transformed cell lines exhibiting specific functions of proximal (RC.SV1) and more distal (RC.SV2) tubule cells (Vandewalle et al., 1989). First, K+ channel equipment surveyed by the patchclamp technique was modified after SV-40 transformation in both cell lines; although a high conductance Ca2+-activated K+ channel [K+200 (Ca2+)] remained the most frequently recorded K+ channel, the transformed state was characterized by emergence of three Ca2+-insensitive K+ channels (150, 50, and 30 pS), virtually absent from primary culture, contrasting with reduced frequency of two Ca2+-sensitive K+ channels (80 and 40 pS). Second, quinine (Q), tetraethylammonium ion (TEA) and charybdotoxin (CTX), at concentrations not affecting cell viability, all decreased H-3-TdR incorporation and cell growth in PC.RC cultures, but only TEA had similar effects in transformed cells. The latter were further characterized by paradoxical effects of Q that induced a marked increase in thymidine incorporation. Q also exerted contrasting effects on channel activity: it inhibited the [K+200 (Ca2+)] when the channel was highly active, with a K(i) (0.2 mM) similar to that measured for H-3-TdR incorporation in PC.RC cells (0.3 mM), but increased the mean current through poorly active channels. TEA blocked all K+ channels with conductance greater-than-or-equal-to 50 pS, including the [K+200 (Ca2+)], in a range of concentrations that substantially affected cell proliferation. The unique effect of TEA on SV-40-transformed cells might be related to broad inhibition of K+ channels.