Abstract
A 50-min treatment of longitudinal smooth muscle of guinea-pig ileum with propylbenzilylcholine mustard (PrBCM, 3 × 10 −6 M) irreversibly inhibited the responses elicited by carbachol. However, a 90-min treatment with PrBCM had no further significant inhibitory effect on the responses to carbachol, suggesting that there are two subtypes of muscarinic cholinoceptors, PrBCM-sensitive and PrBCM-insensitive receptors. Carbachol caused a rapid increase in cytosolic Ca 2+ concentrations ([Ca 2+] i), which was followed by a rapid increase in muscle tension in both untreated and PrBCM-treated preparations. There was a positive correlation between [Ca 2+] i ( R 340 380 ) and tension developed in response to carbachol. A regression line for the two responses was obtained in each preparation. The slope of the line obtained with untreated preparations was steeper than that obtained with PrBCM-treated preparations. These data suggest that, upon activation, PrBCM-sensitive receptors use cytosolic Ca 2+ more effectively than PrBCM-insensitive receptors.
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