Deletion of murine slc29a4 modifies vascular responses to adenosine and 5‐hydroxytryptamine in a sexually dimorphic manner

Abstract

Equilibrative nucleoside transporter 4 (ENT4), encoded by SLC29A4, mediates the flux of both 5‐hydroxytryptamine (5‐HT) and adenosine across cell membranes. We hypothesized that loss of ENT4 function in mice would modify the effects of these established regulators of vascular function. Male and female wild‐type (WT) and slc29a4‐null (ENT4‐KO) mice were compared with respect to their hemodynamics and mesenteric vascular function. Male ENT4‐KO mice had a complete loss of myogenic tone in their mesenteric resistance arteries. This was accompanied by a decrease in blood flow in the superior mesenteric artery in the male ENT4‐KO mice, and a reduced responsiveness to 5‐HT. In contrast, endothelium‐dependent relaxations of mesenteric arteries from female ENT4‐KO mice were more sensitive to Ca2+‐activated K+ (KCa) channel blockade than WT mice. Female ENT4‐KO mice also demonstrated an enhanced vasodilatory response to adenosine in vivo that was not seen in males. Ketanserin (5‐HT2A inhibitor) and GR55562 (5‐HT1B/1D inhibitor) decreased 5‐HT‐induced tone, but only ketanserin inhibited the relaxant effect of 5‐HT in mesenteric arteries. 5‐HT‐evoked increases in tone were elevated in arteries from ENT4‐KO mice upon block of endothelial relaxant pathways, with arteries from female ENT4‐KO mice showing the greatest increase. Adenosine A2b receptor expression was decreased, while other adenosine transporter subtypes, as well as adenosine deaminase and adenosine kinase were increased in mesenteric arteries from male, but not female, ENT4‐KO mice. These findings indicate that deletion of slc29a4 leads to sex‐specific changes in vascular function with significant consequences for regulation of blood flow and pressure by adenosine and 5‐HT.

Uncovering Functional Contributions of PMAT (Slc29a4) to Monoamine Clearance Using Pharmacobehavioral Tools

“…Across psychoactive compounds, our results indicate that PMAT function is sexually dimorphic, a revelation that required perturbations in monoaminergic signaling either via pharmacological mechanisms or by an acute stressor. These findings agree with previous reports that behavioral and physiological consequences of PMAT deficiency emerge in a sex-specific manner following homeostatic perturbations [ 19 , 20 ]. Moreover, the outcomes observed align with current thinking that PMAT is engaged in a compensatory manner, recruited when uptake 1 transporters are saturated and/or incapacitated but otherwise remaining relatively quiescent, and/or exists as a substitute monoamine uptake mechanism in brain regions where uptake 1 transporter expression is scant (e.g., cerebellum, frontal cortex) [ 3 , 9 ].…”

“…Further, we anticipated sex-specific effects would be observed, with females exhibiting augmented sensitization to psychostimulants [ 16 , 17 , 18 ]. Sex-specific effects have been reported across PMAT genotypes as well [ 14 , 19 , 20 ], but given limited evidence in this realm, we did not have any a priori hypotheses regarding directionality of sex × genotype interactions for each drug.…”

“Open Sesame?”: Biomarker Status of the Human Equilibrative Nucleoside Transporter-1 and Molecular Mechanisms Influencing its Expression and Activity in the Uptake and Cytotoxicity of Gemcitabine in Pancreatic Cancer

“…Nucleoside transporters in mammalian cells. CNTs facilitate the Na + -dependent transport while ENTs are bi-directional and Na + -independent transporters, facilitating the uptake of different anticancer drugs [27][28][29][30]. Of note, hENT-1 (es) is NBMPR-sensitive and the figure shows its crystalized structure [30].…”

Summarizing studies using constitutive genetic deficiency to investigate behavioural influences of uptake 2 monoamine transporters

“…Consistent across PMAT studies is evidence that this uptake 2 transporter's function, like OCT3's, is most evident under conditions of disrupted (neuro)physiological homeostasis, whether through environmental stress (forced swim and tail suspension; Table 1) or drug administration (antidepressants and psychostimulants; Table 2). In three of the four studies, evidence supports sex‐specific influences of constitutive PMAT deficiency upon behaviour, 41,42,45 an observation also found with cardiovascular measures 58 . A recent report indicates that PMAT function may be reduced through an estradiol‐mediated signalling mechanism 59 .…”

“…In three of the four studies, evidence supports sex-specific influences of constitutive PMAT deficiency upon behaviour, 41,42,45 an observation also found with cardiovascular measures. 58 A recent report indicates that PMAT function may be reduced through an estradiolmediated signalling mechanism. 59 This might help explain why HT females exhibited more prominent PMAT genotype effects in psychostimulant-induced locomotor sensitization paradigms, 42 but it remains unclear why some behavioural differences are observed in female PMAT KOs but not male PMAT KOs, or vice versa, given there are no functional PMAT to down-regulate in these mice.…”