Twik-2-/- mouse demonstrates pulmonary vascular heterogeneity in intracellular pathways for vasocontractility.

We have previously shown Twik-2-/- mice develop pulmonary hypertension and vascular remodeling. We hypothesized that distal pulmonary arteries (D-PAs) of the Twik-2-/- mice are hypercontractile under physiological venous conditions due to altered electrophysiologic properties between the conduit and resistance vessels in the pulmonary vascular bed. We measured resting membrane potential and intracellular calcium through Fura-2 in freshly digested pulmonary artery smooth muscles (PASMCs) from both the right main (RM-PA) and D-PA (distal) regions of pulmonary artery from WT and Twik-2-/- mice. Whole segments of RM-PAs and D-PAs from 20 to 24-week-old wildtype (WT) and Twik-2-/- mice were also pressurized between two glass micropipettes and bathed in buffer with either arterial or venous conditions. Abluminally-applied phenylephrine (PE) and U46619 were added to the buffer at log increments and vessel diameter was measured. All values were expressed as averages with ±SEM. Vasoconstrictor responses did not differ between WT and Twik-2-/- RM-PAs under arterial conditions. Under venous conditions, Twik-2-/- RM-PAs showed an increased sensitivity to PE with a lower EC50 (P = 0.02). Under venous conditions, Twik-2-/- D-PAs showed an increase maximal vasoconstrictor response to both phenylephrine and U46619 compared to the WT mice (P < 0.05). Isolated PASMCs from Twik-2 -/- D-PA were depolarized and had higher intracellular calcium levels compared to PASMCs from RM-PA of both WT and Twik-2-/- mice. These studies suggest that hypercontractile responses and electrophysiologic properties unique to the anatomic location of the D-PAs may contribute to pulmonary hypertensive vasculopathy.

Hemodynamic and Pathologic Characterization of the TASK-1-/- Mouse Does Not Demonstrate Pulmonary Hypertension.

INTRODUCTION: Pulmonary hypertension (PH) carries significant associated morbidity and mortality and the underlying molecular mechanisms of PH are not well understood. Loss-of-function mutations in TASK-1 potassium channels are associated with PH in humans. Although TASK-1 has been considered in the development of PH for over a decade, characterization of TASK-1 knockout mice has been limited to in vitro studies or in vivo studies in room air at isolated time points. The purpose of this study was twofold. First, we sought to determine if TASK-/- male and female mice developed PH over the span of one year. Second, we sought to determine the effect of chronic hypoxia, a stimulus for PH, and its recovery on PH in TASK-1-/- mice. METHODS: We measured right ventricular systolic pressure (RVSP) and vascular remodeling in male and female C57BL/6 WT and TASK-1-/- mice at separate time points: 20-24 weeks and 1 year of age. Additionally, we measured RVSP and vascular remodeling in TASK-1-/- and wild-type mice between 13 and 16 weeks of age exposed to 10% hypoxia for 3 weeks followed by recovery to room air conditions for an additional 6 weeks. RESULTS: RVSP was similar between WT and TASK-/- mice. Male and female WT and TASK-1-/- mice all demonstrated age-related increases in RVSP, which correlated to age-related vascular remodeling in male mice but not in female mice. Male TASK-1-/- and WT mice exposed to chronic hypoxia demonstrated increased RVSP, which decreased following room air recovery. WT and TASK-1-/- male mice demonstrated vascular remodeling upon exposure to hypoxia that persisted in room air recovery. CONCLUSION: Female and male TASK-1-/- mice do not develop hemodynamic or vascular evidence for PH, but RVSP rises in an age-dependent manner independent of genotype. TASK-1-/- and WT male mice develop hypoxia-induced elevations in RVSP that decrease to baseline after recovery in room air. TASK-1-/- and WT male mice demonstrate vascular remodeling after exposure to hypoxia that persists despite recovery to room air conditions and does not correlate with RVSP normalization.