Connexin Lateralization Contributes to Male Susceptibility to Atrial Fibrillation

Men have a higher risk of developing atrial fibrillation (AF) than women, though the reason for this is unknown. Here, we compared atrial electrical and structural properties in male and female mice and explored the contribution of sex hormones. Cellular electrophysiological studies revealed that action potential configuration, Na⁺ and K⁺ currents were similar in atrial myocytes from male and female mice (4–5 months). Immunofluorescence showed that male atrial myocytes had more lateralization of connexins 40 (63 ± 4%) and 43 (66 ± 4%) than females (Cx40: 45 ± 4%, p = 0.006; Cx43: 44 ± 4%, p = 0.002), with no difference in mRNA expression. Atrial mass was significantly higher in males. Atrial myocyte dimensions were also larger in males. Atrial fibrosis was low and similar between sexes. Orchiectomy (ORC) abolished sex differences in AF susceptibility (M: 65%; ORC: 38%, p = 0.050) by reducing connexin lateralization and myocyte dimensions. Ovariectomy (OVX) did not influence AF susceptibility (F: 42%; OVX: 33%). This study shows that prior to the development of age-related remodeling, male mice have more connexin lateralization and larger atria and atrial myocyte than females. Orchiectomy reduced AF susceptibility in males by decreasing connexin lateralization and atrial myocyte size, supporting a role for androgens. These sex differences in AF substrates may contribute to male predisposition to AF.     

Polyester cure monitoring by means of different techniques

The cure of a set of polyester resin samples having different styrene contents has been monitored by means of Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), rheometry, and ultrasonic measurements. FTIR and DSC experimental data were used to calculate the cure kinetics using a freeradical polymerization model (multiple steps) and also an empirical model that considers the curing to involve only a single step. The dependence of viscosity on the degree of curing has been investigated at different shear rates. Finally, correlations among the results from the different techniques have been established and discussed in terms of the curing mechanism.