Acetylcholine-induced closure of gap junction channels in rat lacrimal glands is probably mediated by protein kinase C

In rat lacrimal gland cells, application of acetylcholine (ACh) opens Ca-dependent channels and closes gap junction channels. We have shown previously that the increase in intracellular calcium concentration induced by ACh, is not required for the closure of gap junctions [20]. We have examined the effects of activators of protein kinase C on gap junction conductance measured with the double patch-clamp technique. This conductance was markedly reduced by incubating the cell pairs for a few minutes with 100 nM phorbol dibutyrate (PdBu). Two membrane permeant analogues of diacylglycerol, OAG (1-oleoyl-2-acetyl-glycerol) and DOG (1,2-dioleoyl-glycerol) also induced a closure of gap junction channels. This effect was observed in the concentration range 10–100 M when the diacylglycerol was added on intact cells, and at 75M when it was applied on dialysed cells. The cell uncoupling was not mediated by phosphatidate, a degradation product of OAG, nor by a phospholipase A₂-induced increase in arachidonate concentration. The OAG-induced closure of gap junction channels reversed spontaneously upon prolonged exposure (more than 90 min at 37°C) to 25 M OAG. After a prolonged OAG treatment, the ability of ACh to uncouple the cells was markedly reduced. ACh induced uncoupling was modulated to some extent by intracellular Ca and had an absolute requirement for Mg. These results indicate that ACh-induced closure of gap junction channels may be mediated by PKC.