The KvLQT1 and minK subunits that coassemble to form I sK channels, contain potential N-glycosylation sites. To examine the role of glycosylation in channel function, a Chinese hamster ovary cell line deficient in glycosylation (Lec-1) and its parental cell line (Pro-5) were transiently transfected with human KvLQT1 (hKvLQT1) cDNA, alone and in combination with the rat (rminK) or human minK (hminK) cDNA. Functional KvLQT1 and I sK currents were expressed in both cell lines, although amplitudes were larger in Pro-5 than Lec-1 cells transfected with hKvLQT1 and hKvLQT1/hminK. For I sK , but not KvLQT1, the voltage-dependence of activation was shifted to more positive voltages and the activation kinetics were slower in the Lec-1 compared to the Pro-5 cells. The effect of extracellular acidification on recombinant KvLQT1 and I sK currents was investigated in Pro-5 and Lec-1 cells. Changing external pH (pH o ) from 7.4 to 6.0 significantly decreased the amplitude and increased the half-activation voltage (V 1/2) of KvLQT1 currents in Pro-5 and Lec-1 cells. In Pro-5 cells, decreasing pH o reduced I sK amplitude without increasing V 1/2, whether rminK or hminK was coexpressed with hKvLQT. In contrast, changing pH o from 7.4 to 6.0 did not significantly change I sK amplitude in Lec-1 cells. Thus, oligosaccharides attached to the minK subunit affect not only the gating properties, but also the pH sensitivity of I sK .
The Journal of Membrane Biology – Springer Journals
Published: Sep 1, 2000
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