Trypsin and α-chymotrypsin treatment abolishes glibenclamide sensitivity of K_ATP channels in rat ventricular myocytes

Cytoplasmic trypsin-treatment of voltagesensitive potassium channels has been shown to cleave domains of the channel responsible for inactivation of the channel. Trypsin has also been reported to remove slow, irreversible inactivation, or run-down in ATP-sensitive potassium (K_ATP) channels. Cytoplasmic treatment of rat ventricular K_ATP channels with either crude, or pure trypsin (1-2 mg/ml) failed to prevent a slow run-down of channel activity. However, trypsin (porcine pancreatic type IX, or type II (Sigma Chem. Co.), or αchymotrypsin (Sigma Chem. Co.) rapidly and irreversibly removed, or substantially decreased glibenclamide and tolbutamide-sensitivity of the channels without removing sensitivity to ATP. We conclude that glibenclamide must bind to either a separate protein, or to a separate domain on the channel in order to effect channel inhibition, and this domain is functionally disconnected from the channel by trypsin-, or α-chymotrypsin treatment.