DEVELOPMENTAL ASPECTS OF EXCITATION-CONTRACTION COUPLING OF RABBIT BLADDER SMOOTH-MUSCLE

There is growing evidence that smooth muscle function changes with nor mal development. In this study a Scatchard analysis revealed that the binding of H-3-ryanodine changed from 6.6 fmol./mg. protein in 3-day-o ld rabbits to 44 fmol./mg. protein in 8-week-old rabbits (p<0.05) with no associated developmental changes-in the dissociation constants. Th e physiological findings using muscle strip techniques correlate well with these findings in that the neonatal bladders are far less sensiti ve to ryanodine than their mature counterparts. In contrast, nifedipin e inhibited contractility in the neonatal group to a much greater degr ee than the mature group. These biochemical and physiological findings support our contention that the mechanism for excitation contraction coupling changes with normal development. Contraction in neonatal rabb it bladder smooth muscle is more dependent upon the influx of extracel lular calcium and with normal maturation mechanisms for intracellular calcium storage and release begin to predominate.