5-(N,N-dimethyl)amiloride-sensitive Na-Li exchange in isolated specimens of human atrium

Pyrethroid Insecticide Cypermethrin Accelerates Pubertal Onset in Male Mice via Disrupting Hypothalamic-Pituitary-Gonadal Axis

Pyrethroids, a class of insecticides that are widely used worldwide, have been identified as endocrine-disrupting chemicals (EDCs). Our recent epidemiological study reported on an association of increased pyrethroids exposure with elevated gonadotropins levels and earlier pubertal development in Chinese boys. In this study, we further investigated the effects of cypermethrin (CP), one of the most ubiquitous pyrethroid insecticides, on hypothalamic-pituitary-gonadal (HPG) axis and pubertal onset in male animal models. Early postnatal exposure to CP at environmentally relevant doses (0.5, 5, and 50 μg/kg CP) significantly accelerated the age of puberty onset in male mice. Administration of CP induced a dose-dependent increase in serum levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone in male mice. CP did not affect gonadotropin-releasing hormone (GnRH) gene expression in the hypothalamus, but CP at higher concentrations stimulated GnRH pulse frequency. CP could induce the secretion of LH and FSH, as well as the expression of gonadotropin subunit genes [chorionic gonadotropin α (CGα), LHβ, and FSHβ] in pituitary gonadotropes. CP stimulated testosterone production and the expression of steroidogenesis-related genes [steroidogenic acute regulatory (StAR) and Cytochrome p 450, family 11, subfamily A, polypeptide 1 (CYP11A1)] in testicular Leydig cells. The interference with hypothalamic sodium channels as well as calcium channels in pituitary gonadotropes and testicular Leydig cells was responsible for CP-induced HPG axis maturation. Our findings established in animal models provide further evidence for the biological plausibility of pyrethroid exposure as a potentially environmental contributor to earlier puberty in males.

Two stable levels of diastolic potential at physiological K+ concentrations in human ventricular myocardial cells

Cells in many specimens of human ventricle can exhibit either of two stable levels of diastolic potential (DP) when exposed to 4 mM K+ in vitro (i.e., -78 +/- 4 mV or -45 +/- 5 mV, mean +/- SEM). In this report we show that the DP of some partially depolarized human ventricular cells developed a sustained 25-35 mV hyperpolarization (n = 28) when bath K+ concentration (K+b) was raised from 4 to 7 mM. On return of K+b to 4 mM, the DP of most, but not all, of these cells returned to the original depolarized levels. In other cells, the transition between the two levels of DP occurred at variable K+b ranging from 1 to 20 mM. We investigated the ionic mechanism(s) underlying the shifts between the two levels of potential by studying the K+ dependence of the DP in partially depolarized cells in 22 specimens of human ventricle. DP hyperpolarized an average of 25.6 mV (from -44.4 +/- 1.3 to -70.0 +/- 1.3 mV; n = 25) when K+b was increased from 4 to 7 mM. Intracellular K+ activity, determined by K+-selective microelectrodes, was within the range of normal reported for other mammalian species (106.7 +/- 4.4 mM in 4 mM K+; n = 22) and was unaffected by increasing K+b to 7 mM (111.7 +/- 6.6 mM; n = 6). Ba2+ (0.05 mM), a blocker of the inward rectifying K+ current, reversibly prevented the hyperpolarization, whereas acetylstrophanthidin (9 microM) failed to inhibit it. These results suggest that the hyperpolarization was due to a K+-dependent increase in K+ permeability and that electrogenic sodium pumping did not contribute significantly to the process. The ionic basis of the depolarization from a hyperpolarized level of DP also was investigated. Decreasing bath Na+ concentration and exposure to 30 microM tetrodotoxin did not prevent the depolarization. However, the depolarization could be inhibited by 2 mM Mn2+. These findings suggest that the depolarization may have been due to a Mn2+-sensitive inward current.