Enteric glia exhibit P2U receptors that increase cytosolic calcium by a phospholipase C-dependent mechanism.
Calcium signaling in fura-2 acetoxymethyl ester-loaded enteric glia was investigated in response to neuroligands; responses to ATP were studied in detail. Carbachol (1 mM), glutamate (100 microM), norepinephrine (10 microM), and substance P (1 microM) did not increase the intracellular calcium concentration ([Ca2+]i) in cultured enteric glia. An increasing percentage of glia responded to serotonin (4%; 100 microM), bradykinin (11%; 10 microM), and histamine (31%; 100 microM), whereas 100% of glia responded to ATP (100 microM). ATP-evoked calcium signaling was concentration dependent in terms of the percentage of glia responding and the peak [Ca2+]i achieved; responses were pertussis toxin insensitive. Based on responsiveness of enteric glia to purinergic agonists and peak [Ca2+]i evoked, ATP = UTP > ADP > beta, gamma-methyleneadenosine 5'-triphosphate >> 2-methylthioadenosine 5'-triphosphate = alpha,beta-methyleneadenosine 5'-triphosphate = AMP = adenosine, suggesting a glial P2U receptor. Depletion of D-myo-inositol 1,4,5-trisphosphate-sensitive calcium stores by thapsigargin (10 microM) abolished glial responses to ATP. Similarly, calcium responses were decreased 92% by U-73122 (10 microM), an inhibitor of phospholipase C, and 93% by the phorbol ester phorbol 12-myristate 13-acetate (100 nM), an activator of protein kinase C. Thus, cultured enteric glia can respond to neurotransmitters with increases in [Ca2+]i. Our data suggest that glial responses to ATP are mediated by a P2U receptor coupled to activation of phospholipase C and release of intracellular calcium stores.
Kimball
B C
BC
Department of Surgery, University of Michigan, Ann Arbor, USA.
Mulholland
M W
MW
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D046508:Culture Techniques; D003600:Cytosol / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D006168:Guinea Pigs; D007150:Immunohistochemistry; D008297:Male; D009197:Myenteric Plexus / Q000378:metabolism*; D009457:Neuroglia / Q000378:metabolism*; D009994:Osmolar Concentration; D037342:Pertussis Toxin; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D058473:Receptors, Purinergic P2Y2; D013729:Terpenes / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D019284:Thapsigargin; D010738:Type C Phospholipases / Q000502:physiology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D018048:Receptors, Purinergic P2; D058473:Receptors, Purinergic P2Y2; D013729:Terpenes; D010566:Virulence Factors, Bordetella; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D037342:Pertussis Toxin; D010738:Type C Phospholipases; D000252:Calcium-Transporting ATPases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium