Potassium depolarized rat uterus in response to oxytocin and its structural analogues: Kinetic analysis

The subject of this communication is the kinetic analysis of dynamic processes in the myometrium of rats in a depolarized state, with a focus on their biomechanics and possible implications in obstetrics. Depolarization was achieved by increasing the concentration of K+ in the organ bath. It is attended by a fast transient increase in muscle tension and the slower establishment of a new resting state in which the phasic component of contractile activity is suppressed. The myometrium remains stimulable by oxytocin and its structural analogues. Time-tonic response profiles indicate participation of several superimposed, time-dependent exponential components whose rate constants reflect transport and distribution routes regulating the intracellular calcium concentration. The initial rapid rise in tension is followed by a slower change to a steady-state level. Its interruption by oil-immersion is followed by an exponential tension decline which allows the determination of the affinity constants of OXT-peptides in the depolarized state. The average potency ratio polarized-to-depolarized myometrium assessed for 11 OXT-peptides, is 9.14. There was no evidence of ligand bias between the two states. Kinetic analysis of the response profiles shows a satisfactory consistency with the reported changes in calcium sensitization and transport processes following OXT stimulation.