Developmental and species differences in the response of the ureter to metabolic inhibition

The effect of inhibiting oxidative phosphorylation on electrically stimulated phasic and high-K+ depolarization-induced tonic contractions in ureteric smooth muscle has been investigated. Intracellular [Ca2+] and pH were monitored fluorimetrically with simultaneous tension measurement, in adult and neonatal rat and guinea-pig ureter. Little difference was found in the response of adult or neonatal rat ureters; cyanide abolished phasic contractions and intracellular Ca2+ transients. The contractions of the adult guinea-pig ureter were also reduced by cyanide, but not as much as those of the adult rat. Neonatal guinea-pig was, however, remarkably resistant to the effects of cyanide, with force and Ca2+ transients remaining at control levels after an initial transient dip. These differences between tissues were not apparent when a high K+ concentration was used to depolarize tissues and produce maintained [Ca2+]i and force changes; cyanide reduced force but not [Ca2+]i in all preparations. Intracellular pH decreased in all preparations with inhibition of oxidative phosphorylation, but this did not correlate with changes in contraction. It is concluded that there are both species and developmental differences in the response to metabolic inhibition of the ureter which lead to differing changes in contractile activity.