Channels for ions and amino acids in kidney cultured cells (MDCK) during volume regulation

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Abstract
A cell line from canine kidney (MDCK) was studied in hypotonic conditions to determine the transport mechanisms involved during regulatory volume decrease (RVD). It was found that RVD was related to a loss of K+, Cl− and amino acids. Membrane potential measurements during RVD have shown a hyperpolarization followed by a depolarization, implying that ion fluxes were probably occurring through channels. Quinine was found to inhibit RVD, the ion fluxes and the amino acid losses. A long preincubation in Ca+ + ‐free EGTA medium had no effect on RVD in cells exposed to the hypotonic medium. Single channel experiments with the patch clamp technique have shown that cell swelling rapidly activates K+ channels and, after a 30 sec delay, Cl− channels. The K+ channel was highly selective and had a linear I‐V curve with a conductance of 25 pS. The Cl− channel was an outward rectifier with conductances of 63 and 26 pS. It was not very selective; replacing Cl− with NO3− did not change the I‐V curve and did not affect RVD. The amino acid losses during RVD were studied with HPLC. It was found that three of them, glutamate, taurine and gly‐cine, had large concentrations and were lost at different rates. Their fluxes during RVD depended linearly on their external concentrations, meaning that the transport process was diffusional. Single channel measurements with glutamate, aspartate or taurine in place of Cl− have shown that these amino acid losses occurred through the Cl− channel.