Functional model for calcium mobilization in the depolarized isolated guinea-pig taenia coli

The muscular response to pharmacological agents is directly dependent on intracellular ionic calcium (Ca2+) and is modulated by membrane permeability and cation-binding to subcellular organelles. The isometric contraction of the ventral guinea-pig taenia coli was registered in a bath with a Rich KCl-Ringer in the absence of Ca2+ and sodium (Na+) with or without EDTA or Sammarium (Sm3+). Our experimental sequence was based on alternate succession between the concentration-response-curves or decay-curves procedure to acetylcholine and barium (Ba2+) in the same preparation. It was found that a contracture elicited by barium ion was not significantly affected by inclusion of EDTA (.01 mM) or Sm3+ (.06 mM). Also, prior exposure of the depolarized muscle to acetylcholine did not affect the barium response. However, prior exposure of the muscle to acetylcholine sensitized the barium-induced contracture to the inhibitory actions of EDTA and Sm3+. Prior exposure of the muscle to barium ions strongly reduced the mechanical response to acetylcholine. In addition, tension recorded during an acetylcholine decay curve was observed to be reduced by EDTA and Sm3+, although some degree of tension could be elicited by acetylcholine even after the depolarized muscle had been exposed to EDTA or Sm3+ up to 70 min. The suggestion is put forward that barium ions mobilize intracellular stores of calcium which may be restored from calcium pools that are mobilized by acetylcholine, EDTA and Sm3+. Acetylcholine would be able to mobilize calcium ions from a firmly bound membrane store and additional less firmly bound membrane stores.(ABSTRACT TRUNCATED AT 250 WORDS)