SPONTANEOUSLY OSCILLATING K-DARBY CANINE KIDNEY-CELLS( CHANNEL ACTIVITY IN TRANSFORMED MADIN)

Intracellular alkalinization is known to be associated with tumorigeni c transformation. Besides phenotypical alterations alkali-transformed Madin-Darby canine kidney (MDCK) cells exhibit a spontaneously oscilla ting cell membrane potential (PD). Using single-channel patch clamp te chniques, it was the aim of this study to identify the ion channel und erlying the rhythmic hyperpolarizations of the PD. In the cell-attache d patch configuration, we found that channel activity was oscillating. The frequency of channel oscillations is 1.1+/-0.1 min-1. At the peak of oscillatory channel activity, single-channel current was -2.7+/-0. 05 pA, and in the resting state it was -1.95+/-0.05 pA. Given the sing le-channel conductance of 53+/-3 pS for inward (and of 27+/-5 pS for o utward) current the difference of single-channel current amplitude cor responded to a hyperpolarization of approximately 14 mV. The channel i s selective for K+ over Na+. Channel kinetics are characterized by one open and by three closed time constants. The channel is Ca2+ sensitiv e. Half maximal activation in the inside-out patch mode is achieved at a Ca2+ concentration of 10 mumol/liter. In addition, we also found a 13-pS K+ channel that shows no oscillatory activity in the cell-attach ed patch configuration and that was not Ca2+ sensitive. We conclude th at the Ca2+-sensitive 53-pS K+ channel is underlying spontaneous oscil lations of the PD. It has virtually identical biophysical properties a s a Ca2+-sensitive K + channel in nontransformed parent MDCK cells. He nce, alkali-induced transformation of MDCK cells did not affect the ch annel protein itself but its regulators thereby causing spontaneous fl uctuations of the PD.