Figure 5.

Effects of the muscarinic agonists on the intracellular Ca²⁺ stores in α-toxin-permeabilized muscle strips. In (a–c), following the loading of the stores with Ca²⁺ by exposure to pCa 5 solution as indicated, 100 μM McN-A343 (a), 100 μM pilocarpine (b) and 10 μM carbachol (CCh) (c) were applied in the absence of extracellular Ca²⁺ but in the presence of 100 μM GTP, which was followed by application of 20 mM caffeine (Caf). The records in (a–c) are from different preparations. In (d), a series of applications of pCa 5, 10 μM CCh, and then 20 mM Caf were repeated three times in a preparation, except in the second trial, the CCh was applied in the presence of 100 μM McN-A343. (e) The summarized results from experiments as in (d). The sizes of CCh- and Caf-evoked tension responses were expressed as percentage of the sustained tension increase by pCa 5 applied for Ca²⁺ loading. Each column indicates mean±s.e.m. of six measurements. *Significantly different (P<0.05) from the corresponding value for control.