Chemical Modification of the Human Ether-a-go-go-related gene(HERG) K* Current by the Amino-Group Reagent Trinitrobenzene Sulfonic Acid

Abstract

We investigated the effects of trinitrobenzene sulfonic acid (TNBS), an amino-group reagent, on the humanether-a-go-go-related gene (HERG) K+ channels expressed inXenopus oocytes. TNBS neutralizes the positively charged amino-agroups of peptideN-terminal and lysine residues. External application of TNBS at 10 mM for 5 min irreversibly shifted the curves for currents at the end of the pulse and tail currents of HERG to a more negative potential and decreased the maximal amplitude of the Itail curve (Itail, max). TNBS had little effect on either the activated current-voltage relationship or the reversal potential of HERG current, indicating that TNBS did not change ion selectivity properties. TNBS shifted the time constant curves of both activation and deactivation of the HERG current to a more hyperpolarized potential; TNBS's effect was greater on channel opening than channel closing. External H+ is known to inhibit HERG current by shifting V1/2 to the right and decreasing Itail, max. TNBS enhanced the blockade of external H+ by exaggerating the effect of H+ on Itail, max, not on V1/2. Our data provide evidence for the presence of essential amino-groups that are associated with the normal functioning of the HERG channel and evidence that these groups modify the blocking effect of external H+ on the current.