Calcium Sensing Receptors Mediate Local Inhibitory Reflexes Evoked by L-Phenylalanine in Guinea Pig Jejunum

Abstract

Amino acids applied to the mucosa evoke inhibitory reflexes in guinea-pig jejunum, but the receptors involved in sensory transduction are still unclear. One promising candidate is the extracellular calcium sensing receptor (CaSR), which is expressed by mucosal enteroendocrine cells and is preferentially activated by aromatic L-amino acids. We tested this by applying various amino acids to the mucosa and recording the resulting inhibitory junction potentials (IJPs) in nearby circular smooth muscle via intracellular recording. The CaSR is stereospecific and L-Phenylalanine evoked a significantly larger response than D-Phenylalanine when both were applied to the same site. The same pattern was seen with L- and D-Tryptophan, another aromatic amino acid. The CaSR is preferentially activated by aromatic amino acids and responses to L-Leucine and L-Lysine were significantly lower than those to L-Phenylalanine applied to the same site. Responses to L-Phenylalanine were dose-dependently suppressed by blockade of the CaSR with NPS2143, a CaSR antagonist, and mimicked by mucosal application of cinacalcet, a CaSR agonist. Responses to cinacalcet had similar pharmacology to that of responses to L-Phenylalanine, in that each requires both P2 purinoreceptors and 5-HT receptors. L-Glutamate evoked IJPs similar to those produced by L-Phenylalanine and these were depressed by blockade of P2 receptors and 5-HT3 plus 5-HT4 receptors, but NPS2143 was ineffective. The AMPA receptor antagonists DNQX (10 μM) and CNQX (10 μM) reduced IJPs evoked by L-Glutamate by 88 and 79% respectively, but neither BAY367260 (mGluR5 antagonist) nor 2APV (NMDA antagonist) affected IJPs evoked by L-Glutamate. We conclude that local inhibitory reflexes evoked by aromatic L-amino acids in guinea pig jejunum involve activation of CaSRs which triggers release of ATP and 5-HT from the mucosa. L-Glutamate also evokes inhibitory reflexes, via a pathway that does not involve CaSRs. It is likely there are multiple receptors acting as sensory transducers for different luminal amino acids.

Calcimimetic acts on enteric neuronal CaSR to reverse cholera toxin-induced intestinal electrolyte secretion

“…Enteric mucosal cells along the entire small and large intestines express the CaSR. These include enterocytes 9 – 12 , neurons in the enteric nervous system (ENS) 9 , 13 and enterochromaffin (EC) cells 14 and other enteroendocrine (EE) cells (refer to a recent review by Tang et al . 15 for refs).…”

Calcium‐sensing receptor regulates intestinal dipeptide absorption via Ca 2+ signaling and IK Ca activation

“…Since external Ca 2+ is the CaSR activator, we further examined if the CaSR is involved in this process. Different concentrations (0.1–30 μM) of NPS‐2143, a selective CaSR antagonist (Gwynne, Ly, Parry, & Bornstein, ; Zhou & Pestka, ), were added to the serosal side of the tissue. As shown in the time course of jejunal Isc (Figure c,d), Gly‐sar induced a significant increase in I sc, which was progressively smaller when the tissue was preincubated with NPS‐2143 in the serosal solution in a dose‐dependent manner.…”

Metabolomics approach: Interpretation of changes in rat plasma metabolites after solifenacin treatment

“…In the literature, it has been reported that l-phenylalanine inhibits circular smooth muscles by activating the extracellular calcium-sensing receptor (CaSR) in the intestines (Gwynne et al, 2017). It can be thought that the decrease in l-phenylalanine level causes constipation from the side effects of solifenacin.…”