Forskolin and antidiuretic hormone stimulate a Ca²⁺-activated K⁺ channel in cultured kidney cells

Single channels in the apical cell membrane of primary cultured chick kidney cells were studied using the patch clamp technique. Cell-attached recordings revealed the presence of a 107 ± 6 pS channel that increased fractional open time upon depolarization. Experiments with inside-out excised patches indicated that the channel is K⁺ selective, Ca²⁺ activated, and inhibited by Ba²⁺. The addition of forskolin or antidiuretic hormone (ADH) to the bath during cell-attached recordings caused an increase in the fractional open time of the channel. The activation of a K⁺ channel by increases in cAMP may be one way in which K⁺ secretion in the kidney is stimulated by ADH in vivo.