CAFFEINE AND MUSCARINIC RECEPTOR AGONIST-SENSITIVE CA2-CELLS( STORES IN CHICK CILIARY GANGLION)

To investigate the presence and the role of intracellular Ca2+, stores in chick ciliary ganglion cells, the concentration of cytosolic free Ca2+ ([Ca]in) was measured in acutely isolated neurons, using fura-2 m icrofluorometry. Caffeine caused a substantial increase in [Ca]in foll owing or during high K+ depolarization: this response was inhibited by treatment of the cells with thapsigargin or with caffeine plus ryanod ine. The peak value and the rate of the depolarization-induced [Ca]in increase were not much altered by either of these treatments, which de plete caffeine-sensitive Ca2+ stores. The muscarinic receptor agonists muscarine, oxotremorine M, and methacholine, caused substantial incre ases in [Ca]in, in a manner that was partially dependent on Ca2+. Thes e agonists also caused a rise in [Ca]in during K+ depolarization, whic h rise was inhibited by treatment with thapsigargin or with caffeine p lus ryanodine. The response to oxotremorine M during depolarization wa s strongly inhibited hy 10 nM 4-DAMP. but was not inhibited by 1 muM p irenzepine or by 1 muM AF-DX 116. These results indicate that chick ci liary ganglion cells possess Ca2+ stores that are activated by both ca ffeine and a second messenger generated by the activation of the M3 mu scarinic receptor subtype.