Description:

This is a neuropharmacological study of muscarinic acetylcholine receptors (mAChRs) in invertebrate (echinoderm) smooth muscle. My work at the BRC has shown echinoderm smooth muscle expresses multiple types of mAChRs (M1, M5) as in mammalian smooth muscle. M1 agonists like oxotremorine M and McNeill-A-343 had the largest effect on both Ca²⁺ flux and contractions suggesting that the echinoderm mAChR is M1-like. Ca²⁺ flux was altered by heparin, LiCl, and myo-inositol indicating that the phosphoinositol pathway was involved in the regulation of Ca²⁺ ions during contraction. Ca²⁺ ATPase inhibitors (cyclopiazonic acid and thapsigarin) and ryanodine receptor agonists (caffeine and ryanodine) all stimulated large Ca²⁺ flux. These data show that in the echinoderm smooth muscle there is a substantial intracellular Ca²⁺ store although it has not been clearly defined since an endoplasmic reticulum is lacking in this smooth muscle preparation. A likely candidate for Ca²⁺ storage is the subsarcolemmic vesicles.