Abstract
The effects of neuraminidase and phospholipase C on the contractility and the Ca++ -binding of guinea pig taenia coli were investigated. Potassium contracture or histamine-induced contracture of taenia coli was inhibited by treatment with neuraminidase, though acetylcholineinduced contracture was not. Treatment with phospholipase C markedly inhibited the contracture induced by isotonic potassium, histamine or acetylcholine. By treatment with neuraminidase for 4hr, about 40 μmol/100mg wet wt of sialic acid was released from taenia coli. This corresponded to two-fifths of total content of sialic acid. By treatment with phospholipase C for 2hr, a similar amount of sialic acid to that produced by neuraminidase treatment was released. The Scatchard plot of Ca++-binding was a biphasic pattern indicating the presence of two types of the Ca++-binding site with different affinity constants. Neuraminidase produced a 57% decrease in the amount of bound Ca++. The Scatchard plot of Ca++-binding changed to a monophasic pattern indicating the disappearance of the low affinity Ca++-binding site. Phospholipase C caused a 59% decrease of bound Ca++. The Scatchard plot also indicated the disappearance of the low affinity Ca++-binding site. From these results, we speculated that sialic acid residue of surface membrane of the muscle cell was first site in the Ca++-influx mechanism.
