A LARGE-CONDUCTANCE CA2-ACTIVATED K+ CHANNEL IN ALPHA-T3-1 PITUITARY GONADOTROPHS()

The Ca2+-activated K+ channel in endocrine cells is responsible for me mbrane hyperpolarization and rhythmic firing of action potentials. The probability of opening of this channel is sensitive to intracellular- free Ca2+ concentration. In this study we have identified one such lar ge conductance Ca2+-activated K+ channel in alpha T3-1 pituitary gonad otroph cell. This channel is ohmic with a unit conductance of 170 pS i n symmetrical KCl (135 mM) and its current reverses near zero millivol ts. When more than one channel is present in the patch membrane they o pen and close independent of each other, exhibiting no cooperativity b etween them as expected of a binomial distribution. The regulatory mec hanism of this channel in modulating hormone secretion from alpha T3-1 gonadotroph cells is indicated.