Given an abstract of a paper, generate a title for this paper such that conveys the key focus of the paper.

Example Input: Abstract: The effects of chronic denervation on sodium (Na) channels in rabbit muscle membrane were determined using intracellular microelectrodes and Vaseline gap voltage clamp techniques. The Hodgkin-Huxley model was used to describe the kinetic and steady-state parameters of channel activation and fast inactivation. Chronic (7-10 days) denervation was found to cause a decreased resting potential, lowered action potential peak, and fibrillation potentials in rabbit extensor digitorum longus (EDL) muscles. Under voltage clamp conditions, no differences were observed between denervated and normal fibers in the voltage dependence of the steady-state Na channel activation and fast inactivation curves, or in the time course of development of fast inactivation. However, in denervated fibers, the time course of recovery from fast inactivation was approximately half that measured in normal fibers. Also, whereas depolarizing holding potentials induced a long-term inactivation to varying degrees in normal EDL fibers, denervated EDL fibers and normal soleus fibers were uniformly resistant to prolonged depolarization. These results suggest that the denervation-induced development of spontaneous activity may be due in part to changes in the mechanisms that control the refractoriness of Na channels.
Example Output: Sodium channel kinetics in normal and denervated rabbit muscle membrane.

Example Input: Abstract: Surgically prepared cryptorchid mouse testes containing only type A spermatogonia were cultured with (Bu)2cAMP in combination with vitamin A (retinol). Treatment with (Bu)2cAMP and retinol for 12-24 h and with basal medium for an additional 8 days stimulated mitotic activity in type A spermatogonia and induced differentiation of germ cells. However, (Bu)2cAMP alone did not induce differentiation of type A spermatogonia. Moreover, when cryptorchid testes were treated with (Bu)2cAMP for longer than 3 days in the presence or absence of retinol, differentiation of type A spermatogonia did not take place; disintegration of the seminiferous tubules occurred instead. When the cryptorchid testes were cultured for 24 h in a medium containing a fixed concentration of retinol and varying concentrations of (Bu)2cAMP from 0.001-0.4 mM, there was a dose-dependent increase in the number of differentiated and mitotic germ cells and type A spermatogonia. Likewise, at a fixed dose of (Bu)2cAMP and increasing concentrations of retinol, a dose-dependent increase in the number of differentiated and mitotic germ cells occurred. However, the number of type A spermatogonia was decreased. The addition of puromycin, cycloheximide, and actinomycin D to the medium completely blocked retinol-(Bu)2cAMP-induced differentiation of the germ cells. The present results suggest that cAMP and retinol trigger biochemical events promoting the synthesis of specific macromolecules involved in the proliferation and differentiation of type A spermatogonia.
Example Output: Dibutyryl adenosine cyclic monophosphate regulates differentiation of type A spermatogonia with vitamin A in adult mouse cryptorchid testis in vitro.

Example Input: Abstract: A reverse hemolytic plaque assay for detecting casein release from individual mammary cells in culture was developed as a bioassay for PRL. Treatment with rat PRL caused dose-related increases in the percentage of mammary cells that released casein and the average size of casein plaques that formed. The assay exhibited exquisite sensitivity (156 fg rat PRL per assay slide) and could be used to evaluate the biopotency of PRL released from individual cells. By combining this "plaque bioassay" with a standard plaque assay for measuring the secretion of immunoreactive PRL, it was possible to compare the bio- and immuno-potencies of hormone released from the same pituitary cells. The results of three separate studies revealed major differences among PRL secretors in these potency estimates. Given the existence of PRL variants with different biological and immunological efficacies, these findings suggest that PRL cells differ from one another in the molecular form(s) of hormone released.
Example Output:
A novel bioassay for lactogenic activity: demonstration that prolactin cells differ from one another in bio- and immuno-potencies of secreted hormone.