Acetylcholine modulation of the conductance of intercellular junctions between rat lacrimal cells.

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Abstract
The conductance of intercellular junctions between rat lacrimal cells was studied with the double whole-cell tight-seal recording technique. This conductance decreases spontaneously with time as a result of the double-cell dialysis. The rate of this ''spontaneous'' uncoupling is unaffected by changing the internal Ca concentration, [Ca]i, between 10-8 M and 10-6 M. This rate of uncoupling is greatly increased when [Ca]i is .apprx. 10-5 M, and this effect does not involve changes in the internal proton concentration. When [Ca]i is weakly buffered in one of the two cells, 1-2 .mu.M-acetylcholine (ACh) both activates Ca-dependent channels in that cell (Marty, Tan and Trautmann, 1984) and uncouples the two cells. The uncoupling is not synchronous with the increase in [Ca]i as reflected by the Ca-dependent currents. When [Ca]i is strongly buffered in both cells. ACh fails to activate Ca-dependent currents, but it can still uncouple the cells. This ACh-induced uncoupling is often preceded by a transient enhancing of the coupling. In conclusion, ACh has several distinct effects on lacrimal cells: (1) activation of Ca-dependent channels in the plasma membrane, (2) closure of junctional channels involving a Ca-independent mechanism, and (3) sometimes, an increase in the junctional coupling by a Ca-independent mechanism.