Influence of chloride and sodium pump activity on carbachol- and acetylaholine-induced depolarizations in denervated rat diphragm.

The effect was measured of low chloride medium and ouabain on carbachol- and acetylcholine-induced depolarizations in denervated rat diaphragm. Membrane potentials were measured in rat diaphragm muscle fibers 10-14 days after denervation. Depolarizations induced by carbachol and acetycholine were increased when the extracellular chloride concentration was diminished from 110 to 40 or 10 mM. Sodium pump inhibition by ouabain (10(-4) M) dramatically enhanced the carbachol depolarizations. In 40 mM Cl- solutions, dose-response relations were determineed with ACh in the absence of presence of dTc. For ACh a pD2 value of 5.2 was found; the pA2 value for dTC appeared to be about 6.4. Therefore, the binding properties of the post-denervational receptors do not appear to be influenced by the chloride gradient. It was concluded that drug-induced depolarizations of the denervated rat diaphragm are short-circuited by chloride ions and counteracted by sodium pumping.