Glycosylation influences gating and pH sensitivity of IsK

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.