Enteric Glia Exhibit P_2U Receptors that Increase Cytosolic Calcium by a Phospholipase C‐Dependent Mechanism

Abstract

Calcium signaling in fura-2 acetoxymethyl ester-loaded enteric glia was investigated in response to neuroligands; responses to AlP were studied in detail. Carbachol (1 mM), glutamate (100 jiM), norepinephrine (10 jiM), and substance P (1 pM) did not increase the intracellular calcium concentration ([Ca 24 ],) in cultured enteric glia. An increasing percentage of glia responded to serotonin (4%; 100 pM), bradykinin (11%; 10 1eM),

Enteric Glia Are Targets of the Sympathetic Innervation of the Myenteric Plexus in the Guinea Pig Distal Colon

“…Second, although guinea pig enteric glia express mGluR5 receptors, stimulation with mGluR agonists (in our hands) does not initiate glial calcium responses (our unpublished observations). In agreement with our findings in situ, Kimball and Mulholland (1996) reported that cultured guinea pig myenteric glia do not respond to glutamate. We also fail to detect enteric glial calcium responses to norepinephrine and muscarinic receptor agonists (our unpublished observation).…”

Presence of functionally active protease‐activated receptors 1 and 2 in myenteric glia

“…All cells responded with D[Ca] i characteristic of this agonist (Kimball and Mulholland 1996). These results are in accordance with previous observations in which primary exposure to the enzyme (thrombin or trypsin) renders the receptor non-responsive to successive agonist exposure.…”

“…As seen in Fig. 10c and previously reported (Kimball and Mulholland 1996), the vast majority of the cells in the culture were glial cells. As a negative control, primary antibodies were replaced with antibody solvent (2% serum in phosphate-buffered saline).…”

“…To demonstrate the specificity of DMS, experiments were performed in which the effects of DMS on ATP-mediated increases in [Ca 2+ ] i were examined. It has been documented previously that ATPmediated increases in [Ca 2+ ] i in enteric glia are solely dependent on PLC activation (Kimball and Mulholland 1996), and therefore would be expected to be independent of sphingosine kinase activity. Exposure of myenteric glia to DMS 1 lM for 5 min did not affect baseline [Ca 2+ ] i .…”

“…Primary cultures of guinea pig myenteric plexus were obtained as described previously (Kimball and Mulholland 1996). Briefly, tenia coli from 1-day-old male Duncan-Hartley guinea pigs (Simonsen, Gilroy, CA, USA) were removed and placed in collagenase for 18-20 h at 4°C, followed by 30 min incubation at 37°C.…”