Response to calcium of skinned gallbladder smooth muscle from newborn and adult guinea pigs.

Guinea pig gallbladder smooth muscle contractility undergoes a period of postnatal maturation. Because tissues from adult animals contract more forcefully than tissues from newborn animals when stimulated with agonists that activate the contractile process through different mechanisms (receptor activation, membrane depolarization), we proposed that factors unrelated to the mechanism of action of the agonist may contribute to the difference in force development between the age groups. Our study tested this hypothesis by examining the in vitro contractile response to calcium of membrane skinned muscle preparations from newborn and adult guinea pigs. Cell membranes were permeabilized using a Triton X-100 (0.5%) skinning solution. The muscle strips were rinsed in relaxing solution then contracted with calcium. The contracting solution contained either 1, 5, 10, or 20 microM calcium. Each muscle strip was stimulated with a single concentration of calcium. The results can be summarized as follows: 1) the maximal response of the skinned preparations did not differ from that of membrane intact preparations; 2) tissues from each age group contracted in a dose-response manner with the maximal response occurring at 10 microM calcium; and 3) at each calcium concentration, tissues from adult animals developed more active force than tissues from newborn animals. The data suggest that the postnatal maturation of gallbladder smooth muscle contractility includes factors involved in calcium activation of the excitation-contraction coupling process.