New biological properties of coffee melanoidins.

Water-soluble melanoidins isolated from roasted coffee induced ex vivo changes in the bioelectric and contractile activity of rat circular gastric smooth muscle tissues. They provoked a depolarization of smooth muscle cellular membranes and an increase in Ca²⁺-influx as evidenced by the increase in the frequency and amplitude of Ca²⁺-generated spike potentials. In the presence of 1 × 10⁻⁶ mol L⁻¹ acetylcholine and 1 × 10⁻⁶ mol L⁻¹ arecoline the melanoidin-evoked contraction was significantly reduced. M-cholinergic receptor blocking agents atropine, ipratropium, pirenzepine, and 4-DAMP also significantly reduced the melanoidin-provoked contraction. Nonspecific N-cholinergic receptor blockers hexamethonium and decamethonium (1 × 10⁻⁵ mol L⁻¹ each) did not influence the melanoidin-induced mechanical reaction. The melanoidins did not affect the strength of contractions evoked by adrenaline and dopamine (1 × 10⁻⁶ mol L⁻¹ each). The results obtained support the assumption that melanoidin-evoked contraction is a result of activation of muscarinic-type cholinergic receptors.