Glycosylation influences gating and pH sensitivity of I(sK)

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).