Stimulus-permeability coupling in rat lacrimal gland

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Abstract
Incubation of isolated cells wtih 10(-2) M ethylene glycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid or cobalt inhibits 22Na and 45Ca uptake stimulated by carbachol. The artificial introduction of Ca into the cytosol by the cation ionophore A23187 also initiates the 22Na uptake. Amiloride (10(-5) M) partially inhibits 22Na uptake induced by carbachol, but has no effect on receptor-stimulated 45Ca uptake or 86Rb release. Tetrodotoxin (TTX) has no effect on 22Na uptake stimulated by carbachol, whereas methoxyverapamil (D 600) produces a small but significant decrease in both 22Na and 45Ca uptake. This effect of D 600 may be related to a block of receptor activation and not to a block of Ca channel activation. Incubation in high K (56 mM) does not prevent the change in membrane permeability to Ca, K, and Na initiated by carbachol. It is concluded that carbachol stimulates the influx of Ca; the rise in the cytosolic Ca concentration then couples receptor activation to a change in membrane permeability to K and Na. The permeability mechanisms for Ca, K, and Na that are activated by carbachol appear to be specific for each of the three cations and appear to be dissimilar to permeability mechanisms in excitable tissue that carry the same ions.