Brugada syndrome trafficking-defective Nav1.5 channels can trap cardiac Kir2.1/2.2 channels.

Cardiac Nav1.5 and Kir2.1-2.3 channels generate Na (INa) and inward rectifier K (IK1) currents, respectively. The functional INa and IK1 interplay is reinforced by the positive and reciprocal modulation between Nav15 and Kir2.1/2.2 channels to strengthen the control of ventricular excitability. Loss-of-function mutations in the SCN5A gene, which encodes Nav1.5 channels, underlie several inherited arrhythmogenic syndromes, including Brugada syndrome (BrS). We investigated whether the presence of BrS-associated mutations alters IK1 density concomitantly with INa density. Results obtained using mouse models of SCN5A haploinsufficiency, and the overexpression of native and mutated Nav1.5 channels in expression systems - rat ventricular cardiomyocytes and human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) - demonstrated that endoplasmic reticulum (ER) trafficking-defective Nav1.5 channels significantly decreased IK1, since they did not positively modulate Kir2.1/2.2 channels. Moreover, Golgi trafficking-defective Nav1.5 mutants produced a dominant negative effect on Kir2.1/2.2 and thus an additional IK1 reduction. Moreover, ER trafficking-defective Nav1.5 channels can be partially rescued by Kir2.1/2.2 channels through an unconventional secretory route that involves Golgi reassembly stacking proteins (GRASPs). Therefore, cardiac excitability would be greatly affected in subjects harboring Nav1.5 mutations with Golgi trafficking defects, since these mutants can concomitantly trap Kir2.1/2.2 channels, thus unexpectedly decreasing IK1 in addition to INa.

Optimizing human semen cryopreservation by reducing test vial volume and repetitive test vial sampling.

OBJECTIVE: To investigate optimal test vial (TV) volume, utility and reliability of TVs, intermediate temperature exposure (-88°C to -93°C) before cryostorage, cryostorage in nitrogen vapor (VN2) and liquid nitrogen (LN2), and long-term stability of VN2 cryostorage of human semen. DESIGN: Prospective clinical laboratory study. SETTING: University assisted reproductive technology (ART) laboratory. PATIENT(S): A total of 594 patients undergoing semen analysis and cryopreservation. INTERVENTION(S): Semen analysis, cryopreservation with different intermediate steps and in different volumes (50-1,000 µL), and long-term storage in LN2 or VN2. MAIN OUTCOME MEASURE(S): Optimal TV volume, prediction of cryosurvival (CS) in ART procedure vials (ARTVs) with pre-freeze semen parameters and TV CS, post-thaw motility after two- or three-step semen cryopreservation and cryostorage in VN2 and LN2. RESULT(S): Test vial volume of 50 µL yielded lower CS than other volumes tested. Cryosurvival of 100 µL was similar to that of larger volumes tested. An intermediate temperature exposure (-88°C to -93°C for 20 minutes) during cryopreservation did not affect post-thaw motility. Cryosurvival of TVs and ARTVs from the same ejaculate were similar. Cryosurvival of the first TV in a series of cryopreserved ejaculates was similar to and correlated with that of TVs from different ejaculates within the same patient. Cryosurvival of the first TV was correlated with subsequent ARTVs. Long-term cryostorage in VN2 did not affect CS. CONCLUSION(S): This study provides experimental evidence for use of a single 100 µL TV per patient to predict CS when freezing multiple ejaculates over a short period of time (<10 days). Additionally, semen cryostorage in VN2 provides a stable and safe environment over time.