AJP - Gastrointestinal and Liver Physiology, Vol 272, Issue 3 463-G473, Copyright © 1997 by American Physiological Society

ARTICLES

Purinergic Ca2+ signaling in myenteric neurons via P2 purinoceptors

F. L. Christofi, Z. Guan, J. D. Wood, L. V. Baidan and B. T. Stokes
Department of Anesthesiology, College of Medicine, The Ohio State University, Columbus 43210, USA.

Fura 2 microfluorimetry was used to test the hypothesis that ATP acts at P1 and P2 purinoceptors to elevate cytosolic free Ca2+ concentrations [Ca2+]i) in calbindin-immunoreactive cultured myenteric neurons from adult guinea pig small intestine. Local "micro-puff" application of ATP or ATP(gamma)S caused an increase in [Ca2+]i in 99% of 200 multipolar neurons. The potency profile of agonists for the rise in [Ca2+]i was ATP(gamma)S = ATP >> ADP >> AMP, adenosine, 5'-(N-ethylcarboxamido)adenosine, and 2-chloro-N(6)-cyclopentyladenosine. Tetrodotoxin-sensitive synaptic transmission could contribute as much as 25% to the ATP response. The P1 antagonist 8-cyclopentyl-1,3-dipropylxanthine blocked 50% of the peakATP Ca2+ response. P2 antagonists blocked the ATP response: pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid > reactive blue 2 > suramin. Suramin enhanced the ATP response in 27.5% of neurons. Some neurons (<15%) displayed distinct multiphasic Ca2+ signatures. About 54% of ATP-responsive neurons expressed calbindin. The data support the following hypotheses: 1) two distinct P2 purinoceptors are linked to the rise in [Ca2+]i in myenteric neurons; 2) purinergic Ca2+ signaling is not restricted to one neuronal phenotype; and 3) intraneuronal Ca2+ is not involved in adenosinergic hyperpolarization in AH/type 2 neurons.

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