Cholecystokinin B-type receptors mediate a G-protein-dependent depolarizing action of sulphated cholecystokinin ocatapeptide (CCK-8s) on rodent neonatal spinal ventral horn neurons

Cholecystokinin octapeptide antagonizes apoptosis in human retinal pigment epithelial cells

Although cholecystokinin octapeptide-8 is important for neurological function, its neuroprotective properties remain unclear. We speculated that cholecystokinin octapeptide-8 can protect human retinal pigment epithelial cells against oxidative injury. In this study, retinal pigment epithelial cells were treated with peroxynitrite to induce oxidative stress. Peroxynitrite triggered apoptosis in these cells, and increased the expression of Fas-associated death domain, Bax, caspa-se-8 and Bcl-2. These changes were suppressed by treatment with cholecystokinin octapeptide-8. These results suggest that cholecystokinin octapeptide-8 can protect human retinal pigment epithelial cells against apoptosis induced by peroxynitrite.

Effects of endogenous cannabinoid anandamide on excitation-contraction coupling in rat ventricular myocytes

A role for anandamide (N-arachidonoyl ethanolamide; AEA), a major endocannabinoid, in the cardiovascular system in various pathological conditions has been reported in earlier reports. In the present study, the effects of AEA on contractility, Ca2+ signaling, and action potential (AP) characteristics were investigated in rat ventricular myocytes. Video edge detection was used to measure myocyte shortening. Intracellular Ca2+ was measured in cells loaded with the fluorescent indicator fura-2 AM. AEA (1 μM) caused a significant decrease in the amplitudes of electrically evoked myocyte shortening and Ca2+ transients. However, the amplitudes of caffeine-evoked Ca2+ transients and the rate of recovery of electrically evoked Ca2+ transients following caffeine application were not altered. Biochemical studies in sarcoplasmic reticulum (SR) vesicles from rat ventricles indicated that AEA affected Ca2+ -uptake and Ca2+ -ATPase activity in a biphasic manner. [3H]-ryanodine binding and passive Ca2+ release from SR vesicles were not altered by 10 μM AEA. Whole-cell patch-clamp technique was employed to investigate the effect of AEA on the characteristics of APs. AEA (1 μM) significantly decreased the duration of AP. The effect of AEA on myocyte shortening and AP characteristics was not altered in the presence of pertussis toxin (PTX, 2 μg/ml for 4 h), AM251 and SR141716 (cannabinoid type 1 receptor antagonists; 0.3 μM) or AM630 and SR 144528 (cannabinoid type 2 receptor antagonists; 0.3 μM). The results suggest that AEA depresses ventricular myocyte contractility by decreasing the action potential duration (APD) in a manner independent of CB1 and CB2 receptors.

Cholecystokinin: a multi-functional molecular switch of neuronal circuits

Cholecystokinin (CCK), a peptide originally discovered in the gastrointestinal tract, is one of the most abundant and widely distributed neuropeptides in the brain. In spite of its abundance, recent data indicate that CCK modulates intrinsic neuronal excitability and synaptic transmission in a surprisingly cell-type specific manner, acting as a key molecular switch to regulate the functional output of neuronal circuits. The central importance of CCK in neuronal networks is also reflected in its involvement in a variety of neuropsychiatric and neurological disorders including panic attacks and epilepsy.

Cell-type-specific CCK2 receptor signaling underlies the cholecystokinin-mediated selective excitation of hippocampal parvalbumin-positive fast-spiking basket cells

Parvalbumin-positive (PV+) fast-spiking basket cells are thought to play key roles in network functions related to precise time keeping during behaviorally relevant hippocampal synchronous oscillations. Although they express relatively few receptors for neuromodulators, the highly abundant and functionally important neuropeptide cholecystokinin (CCK) is able to selectively depolarize PV+ basket cells, making these cells sensitive biosensors for CCK. However, the molecular mechanisms underlying the CCK-induced selective and powerful excitation of PV+ basket cells are not understood. We used single and paired patch-clamp recordings in acute rat hippocampal slices, in combination with post hoc identification of the recorded interneurons, to demonstrate that CCK acts via G-protein-coupled CCK2 receptors to engage sharply divergent intracellular pathways to exert its cell-type-selective effects. In contrast to CCK2 receptors on pyramidal cells that signal through the canonical G(q)-PLC pathway to trigger endocannabinoid-mediated signaling events, CCK2 receptors on neighboring PV+ basket cells couple to an unusual, pertussis-toxin-sensitive pathway. The latter pathway involves ryanodine receptors on intracellular calcium stores that ultimately activate a nonselective cationic conductance to depolarize PV+ basket cells. CCK has highly cell-type-selective effects even within the PV+ cell population, as the PV+ dendrite-targeting bistratified cells do not respond to CCK. Together, these results demonstrate that an abundant ligand such as CCK can signal through the same receptor in different neurons to use cell-type-selective signaling pathways to provide divergence and specificity to its effects.