TRPM4 Couples Mechanical Force to Myogenic Constriction Throughout the Resistance Vasculature
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Background
Myogenic tone is a fundamental property of resistance arteries that stabilizes tissue perfusion by coupling intraluminal pressure to smooth muscle cell (SMC) depolarization, Ca 2+ influx, and vasoconstriction. TRPM4 (transient receptor potential melastatin 4) cation channels are required for this response in cerebral arteries, but whether TRPM4-dependent mechanotransduction is conserved across the broader resistance vasculature has remained unknown.
Methods
We combined droplet digital PCR, a newly generated Trpm4 -Cre transgenic reporter mouse line, native-cell patch-clamp electrophysiology, pressure myography, selective pharmacological inhibition, and novel SMC-specific Trpm4 -knockout ( Trpm4 -smKO) mice to define the expression, regulation, and functional importance of TRPM4 in cerebral, mesenteric, and skeletal muscle resistance arteries.
Results
Trpm4 transcripts were detected in all three vascular beds, and genetic reporter-based mapping localized TRPM4 expression to SMCs in multiple organs. Using conventional whole-cell patch-clamp electrophysiology, we recorded cation currents activated by high intracellular [Ca 2+ ] and sensitive to the selective TRPM4 blocker 4-chloro-2-(1-naphthyloxyacetamido) benzoic acid (NBA) in native SMCs from all three beds. In cells patch-clamped using the amphotericin B-perforated configuration, stretching the plasma membrane by applying negative pressure (-20 mmHg) through the patch pipette activated transient inward cation currents that were suppressed by NBA. The selective angiotensin II type 1 receptor (AT 1 R) blocker losartan also inhibited stretch-induced currents without affecting Ca 2+ -activated whole-cell TRPM4 currents, indicating that AT 1 R signaling is required for mechanotransduction in SMCs from all three vascular beds. In pressurized arteries with established myogenic tone, NBA produced reversible, concentration-dependent suppression of pressure-induced constriction of cerebral, mesenteric, and skeletal muscle arteries while sparing constriction induced by direct depolarization of SMCs with high (60 mM) extracellular [K + ]. TRPM4-dependent whole-cell currents and stretch-induced cation currents were decreased in SMCs from Trpm4 -smKO mice, and myogenic tone was essentially absent in all three vascular beds from these animals.
Conclusions
These findings show that TRPM4 is essential for pressure-induced SMC depolarization and myogenic constriction in the resistance vasculature.
