The changes in dietary constituents during growth and development from predominantly liquid to mixed solid liquid meals places an increasing burden on the antrum, which is required to triturate solids. The authors hypothesize that concomitant with these changing dietary constituents different pathways are used to mediate contraction in response to acetylcholine. Smooth muscle cells were isolated by collagenase digestion from the fundus and circular muscle layer of the antrum in the adult cat and 1-week-old kitten. The unstimulated cells from the fundus and antrum were larger in the adult than in the kitten. In normal physiological salt solution, all cells contracted in a similar dose dependent manner in response to acetylcholine in both age groups. Fundic muscle cell contraction in response to acetylcholine was unchanged in calcium-free physiological salt solution or in the presence of the calcium channel blocker, methoxyverapamil. In the adult, antral cells contracted 50% less in the absence of extracellular calcium. In the kitten, antral cells did not contract under the same conditions. After permeabilization with saponin, fundic muscle cells from the adult and kitten contracted fully in response to 1,4,5-inositol trisphosphate, whereas contraction of adult antral cells was reduced by 50% and contraction of kitten antral cells was completely blocked. These data suggest that isolated muscle cells from the fundus of both the adult cat and newborn kitten use intracellular calcium stores to contract in response to acetylcholine and 1,4,5-inositol triphosphate. In adult antral cells, acetylcholine-induced contraction requires both influx of extracellular calcium and release of intracellular calcium. In kitten antral cells, intracellular calcium stores are not used or available to mediate contraction in response to acetylcholine.
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