Excitation-Contraction Coupling in Ureteric Smooth Muscle: Mechanisms Driving Ureteric Peristalsis

Products of oxidative and non-oxidative metabolism of L-arginine as potential regulators of Ca2+ transport in mitochondria of uterine smooth muscle

Mitochondria play a crucial role in maintaining Ca2+ homeostasis in cells. Due to the critical regulatory role of the products of oxidative and non-oxidative metabolism of L-arginine, it is essential to clarify their effect on Ca2+ transport in smooth muscle mitochondria. Experiments were performed on the uterine myocytes of rats and isolated mitochondria. The possibility of NO synthesis by mitochondria was demonstrated by confocal microscopy and spectrofluorimetry methods using the NO-sensitive fluorescent probe DAF-FM and Mitotracker Orange CM-H2TMRos. It was shown that 50 μM L-arginine stimulates the energy-dependent accumulation of Ca2+ in mitochondria using the fluorescent probe Fluo-4 AM. A similar effect occurred when using nitric oxide donors 100 μM SNP, SNAP, and sodium nitrite (SN) directly. The stimulating effect was eliminated in the presence of the NO scavenger C-PTIO. Nitric oxide reduces the electrical potential in mitochondria without causing them to swell. The stimulatory effect of spermine on the accumulation of Ca2+ by mitochondria is attributed to the enhancement of NO synthesis, which was demonstrated with the use of C-PTIO, NO-synthase inhibitors (100 μM NA and L-NAME), as well as by direct monitoring of NO synthesis fluorescent probe DAF-FM. A conclusion was drawn about the potential regulatory effect of the product of the oxidative metabolism of L-arginine - NO on the transport of Ca2+ in the mitochondria of the myometrium, as well as the corresponding effect of the product of non-oxidative metabolism -spermine by increasing the synthesis of NO in these subcellular structures.

TRPM3 channel activation inhibits contraction of the isolated human ureter via CGRP released from sensory nerves

AIMS

Sensory nerve activation modulates ureteral contractility by releasing neuropeptides including CGRP and neurokinin A (NKA). TRPM3 is a recently discovered thermosensitive channel expressed in nociceptive sensory neurons, and plays a key role in heat nociception and chronic pain. The aim of this study is to examine the role of TRPM3 activation in human ureter motility.

MAIN METHOD

Human proximal ureters were obtained from fourteen patients undergoing nephrectomy. Spontaneous or NKA-evoked contractions of longitudinal ureter strips were recorded in an organ bath. Ureteral TRPM3 expression was examined by immunofluorescence.

KEY FINDINGS

Spontaneous contractions were observed in 60% of examined strips. TRPM3 activation using pregnenolone sulphate (PS) or CIM0216 (specific TRPM3 agonists) dose-dependently reduced the frequency of spontaneous and NKA-evoked contractions, with IC50s of 241.7 μM and 4.4 μM, respectively. The inhibitory actions of TRPM3 agonists were mimicked by CGRP (10 to 100 nM) or a cAMP analogue (8-Br-cAMP; 1 mM). The inhibitory actions of TRPM3 agonists (300 μM PS or 30 μM CIM0216) were blocked by pretreatment with primidone (TRPM3 antagonist; 30 μM), tetrodotoxin (sodium channel blocker; 1 μM), olcegepant (CGRP receptor antagonist; 10 μM), or H89 (non-specific PKA inhibitor; 30 μM). TRPM3 was co-expressed with CGRP in nerves in the sub-urothelial and intermuscular regions of the ureter.

SIGNIFICANCE

TRPM3 channels expressed on sensory terminals of the human ureter involve in inhibitory sensory neurotransmission and modulate ureter motility via the CGRP-cAMP-PKA signal pathway. Targeting TRPM3 may be a pharmacological strategy for promoting the ureter stone passage.

The Urothelium: Life in a Liquid Environment

The urothelium, which lines the renal pelvis, ureters, urinary bladder, and proximal urethra, forms a high-resistance but adaptable barrier that surveils its mechanochemical environment and communicates changes to underlying tissues including afferent nerve fibers and the smooth muscle. The goal of this review is to summarize new insights into urothelial biology and function that have occurred in the past decade. After familiarizing the reader with key aspects of urothelial histology, we describe new insights into urothelial development and regeneration. This is followed by an extended discussion of urothelial barrier function, including information about the roles of the glycocalyx, ion and water transport, tight junctions, and the cellular and tissue shape changes and other adaptations that accompany expansion and contraction of the lower urinary tract. We also explore evidence that the urothelium can alter the water and solute composition of urine during normal physiology and in response to overdistension. We complete the review by providing an overview of our current knowledge about the urothelial environment, discussing the sensor and transducer functions of the urothelium, exploring the role of circadian rhythms in urothelial gene expression, and describing novel research tools that are likely to further advance our understanding of urothelial biology.