Unusual calcium-activated potassium channels of bovine parathyroid cells

Parathyroid cells have unusual responses to an increase in the external calcium concentration--a reduction in secretion and a depolarization. In an attempt to explain this behavior, we have studied voltage-clamped inside-out patches from bovine parathyroid cells. We found a potassium-selective channel that requires internal calcium to open and has a 175-pS conductance. This channel differs from calcium-activated potassium channels that have been found in other cells in that it closes when the internal calcium concentration is increased above about 160 nM. This channel can account for the depolarization that occurs in parathyroid cells in high-calcium solutions. It may also account for the reduced secretion in high-calcium solutions.