Developmental aspects of excitation contraction coupling of rabbit bladder smooth muscle.

There is growing evidence that smooth muscle function changes with normal development. In this study a Scatchard analysis revealed that the binding of 3H-ryanodine changed from 6.6 fmol./mg. protein in 3-day-old rabbits to 44 fmol./mg. protein in 8-week-old rabbits (p < 0.05) with no associated developmental changes in the dissociation constants. The physiological findings using muscle strip techniques correlate well with these findings in that the neonatal bladders are far less sensitive to ryanodine than their mature counterparts. In contrast, nifedipine inhibited contractility in the neonatal group to a much greater degree 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 rabbit bladder smooth muscle is more dependent upon the influx of extracellular calcium and with normal maturation mechanisms for intracellular calcium storage and release begin to predominate.