Calcium-activated potassium channels in chondrocytes

The presence of calcium-activated potassium channels in chondrocytes of growing cartilage was tested. Results obtained with fura-2 on cultured resting chondrocytes indicate that the cells respond to an elevation of extracellular calcium concentration ( [Ca²⁺]_o ) from 0.1 to 2 mM increasing the intracellular concentration of the ion ( [Ca²⁺]_i ) from 117 to 187 nM. This increment may be blocked by 3μM La³⁺. Patch clamp experiments in cell-attached configuration showed that, when [Ca²⁺]_i rises, the open probability (Po) of the K⁺ channels increases. Increments in both Po and unitary currents of the K⁺ channels can be obtained after applying 2.5μM A23187 with 2mM [Ca²⁺]_o. Hence, the results demonstrate that, in chondrocytes, a class of Ca²⁺-activated K⁺ channels is present and their activity is related to an increase of [Ca²⁺]_i.