Recordings have been made of a potassium-selective ion channel in primary cultures of cells derived from explants of human eccrine sweat glands obtained from normal subjects and from subjects suffering from cystic fibrosis. There appears to be no functional difference between potassium channels derived from normal subjects and those from cystic fibrosis subjects. The channel falls into the group generally known as "Maxi-K" channels, and has a slope conductance, with symmetrical solutions in bath and pipette containing 140 mM K+, of approximately 230 pS. It is calcium-activated, pH-sensitive and can be blocked by barium and quinine. The channel appears only very rarely in patches derived from confluent cells (in approximately 1 in 30 patches containing channels), but it is more frequently observed in younger cultures of dividing cells derived from recently explanted (within the previous 48-72 h) glands. It is possible that this channel is normally located on the basolateral membrane of the cell, and is responsible for the calcium-dependent secretory and absorptive events seen in the intact sweat gland.
Barium Calcium