Electrical and mechanical properties of smooth muscle cells of the guinea pig biliary system

The membrane potentials of the smooth muscle cells of the sphincter of Oddi, gall bladder or common bile duct of the guinea pig was --56, --40 or --54 mV, respectively. The length constant of the tissue of the sphincter of Oddi was 1.7 mm and this value was larger than that measured in hypertonic solution. The smooth muscle cells of the gall bladder and common bile duct were always spontaneously active, while this was not the case with cells from the sphincter of Oddi, nevertheless, electrical stimulation consistently produced spike generation. Acetylcholine depolarized the membrane and increased the spike frequency in muscle cells of the sphincter of Oddi, gall bladder and common bile duct. However, noradrenaline produced alpha-adrenergic inhibitory action in the sphincter of Oddi and common bile duct, and alpha-adrenergic excitatory action in the gall bladder. Isoprenaline, a beta-adrenergic agent, induced an inhibitory action in the above three regions. Prostaglandin E1 (PGE1) suppressed the membrane activity in the sphincter of Oddi, and this response was similar to that observed in the circular muscle of the intestine. In the gall bladder, PGE1 accelerated the membrane activity. Gastrin and secretin did not affect the smooth muscle activity of the gall bladder but these agents slightly suppressed electrical and mechanical activities in the sphincter of Oddi. On the other hand, cholecystokinin markedly accelerated the electrical and mechanical activities in the gall bladder but these actions were weak in the sphincter of Oddi. Muscle properties of the smooth muscle cells of the biliary system are discussed in relation to the mechanism of bile expulsion through the sphincter of Oddi.