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.