A CATIONIC CHANNEL REGULATED BY A VERTEBRATE INTRINSIC CIRCADIAN OSCILLATOR

SECRETORY cells of the chicken pineal gland exhibit light sensitive ci rcadian rhythms in melatonin release that persist in vitro(1-12). Mela tonin secretion is positively regulated by cyclic AMP and intracellula r Ca2+ (refs 8, 10-15), Cyclic AMP analogues are more effective at sti mulating melatonin secretion during the circadian night owing in part to increased Ca2+ influx at those times(12), However, this cannot be a ttributed to increased activity of L-type Ca2+ channels(12). Here we d escribe an unusual 40-pS cationic channel (I-LOT) in cultured chicken pineal cells that is permeable to Ca2+ and active in the night but not during the day, I-LOT is not voltage- or stretch-activated, it has a characteristically long open time, and its gating persists in excised inside-out patches in the absence of Ca2+ or cyclic nucleotides. Daily rhythms in I-LOT gating are also observed in previously entrained chi cken pineal cells free-running under constant dark conditions. Nightti me I-LOT activity is not suppressed by brief Light pulses.