1. A possible role for the ATP-sensitive potassium channels in the pathogenesis of hypokalaemic periodic paralysis was investigated.

2. We assessed insulin release and muscle strength after intravenous glucose loading with and without the potassium channel opener pinacidil and the potassium channel blocker glibenclamide in three patients with hypokalaemic periodic paralysis and in a pair of matched control subjects for each patient.

3. A significantly higher initial insulin response (1.5-30 min) was found in the patients with hypokalaemic periodic paralysis in comparison with the control subjects. During potassium channel blocking with glibenclamide the insulin release was more enhanced in patients than in control subjects. On the other hand, the potassium channel opener pinacidil impaired the insulin release in healthy control subjects but not in patients. The serum glucose levels showed no differences between patients and control subjects. In one of the patients with hypokalaemic periodic paralysis glucose loading resulted in a fall in muscle strength, which did not occur during the administration of pinacidil.

4. These findings suggest a disturbance in the ATP-sensitive potassium channel in patients with hypokalaemic periodic paralysis, which is not limited to pancreatic β cells, but may be also involved in the abnormal behaviour of skeletal muscle.