Introduction: TRPM3 is a non-selective cation channel activated by pregnenolone sulfate (PS). PS contracts mouse aorta by activating TRPM3 in vascular smooth muscle cells (VSMCs)¹. However, PS induces vasodilation in mesenteric arteries by activating channels present in the adventitial sensory nerve endings². These opposing effects preclude an explanation of the role of TRPM3 channels in the control of blood pressure (BP), hindering their potential role as novel therapeutical targets against hypertension.

Aims: Here we explored the vascular phenotype of a TRPM3-KO mice and we analyzed the potential contribution of TRPM3 channels to renal control of BP, exploring their expression in kidneys and their role in renal blood flow regulation.

Methods: TRPM3-KO mice and their corresponding WT littermates were used for this study. BP measurements were carried out in awake animals with tail-cuff CODA^® system. Mice were anesthetized by isoflurane inhalation (5% O2 at 2.5 Lmin-1) and sacrificed by cervical dislocation, following the EC guiding principles regarding the care and use of animals (Directive 2010/63/UE). Renal TRPM3 expression was measured with qPCR, and channel location throughout the nephron was studied combining RNAscope^TM with immunohistochemistry. The functional contribution of TRPM3 in renal vasculature was analyzed by exploring the effect of PS in renal flow at constant pressure in isolated kidneys in organ bath.

Results : BP measurements showed that TRPM3-KO mice were hypotensive and resistant to angiotensin II-induced hypertension, which could be explained by renal modulation of the RAAS system by TRPM3. In support of this, qPCR showed a 2-fold increase in TRPM3 mRNA expression in kidneys from hypertensive BPH mice. TRPM3 mRNA expression was detected in the glomeruli, the distal convoluted tubule (DCT) and the collecting ducts (CD), but not in renal vessels. 10µM PS-induced vasodilation was observed in basal conditions and in the presence of Phenylephrine. The effect of PS was fully abolished by BIBN-4096 (a CGRP antagonist) or the NOS blocker L-NAME, but was unaffected by COX inhibition with Indomethacin.

Conclusions: We suggest that TRPM3 at perivascular nerve endings contributes to renal flow regulation through an CGRP- and NO-dependent pathway, while TRPM3 at the nephron could be involved in BP regulation via tubule-glomerular feedback, contributing to the hypotensive phenotype of TRPM3-KO.