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Activation of the phospholipase C pathway by ATP is mediated exclusively through nucleotide type P 2 ‐purinoceptors in C2C12 myotubes
Author(s) -
Henning Robert H.,
Duin Marry,
Hertog Adriaan,
Nelemans Adriaan
Publication year - 1993
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1993.tb13875.x
Subject(s) - suramin , purinergic receptor , p2y receptor , nucleotide , ppads , adenosine triphosphate , adenosine , chemistry , inositol , myogenesis , phospholipase c , inositol phosphate , adenine nucleotide , receptor , medicine , endocrinology , biology , biochemistry , myocyte , gene
1 The presence of a nucleotide receptor and a discrete ATP‐sensitive receptor on C2C12 myotubes has been shown by electrophysiological experiments. In this study, the ATP‐sensitive receptors of C2C12 myotubes were further characterized by measuring the formation of inositol(1,4,5)trisphosphate (Ins(1,4,5)P 3 ) and internal Ca 2+ . 2 The nucleotides ATP and UTP caused a concentration‐dependent increase in Ins(1,4,5)P 3 content with comparable time courses (EC 50 : ATP 33 ± 2 μ m , UTP 80 ± 4 μ m ). ADP was less effective in increasing Ins(1,4,5)P 3 content of the cells, while selective agonists for P 1 ‐, P 2X ‐ and P 2Y ‐purinoceptors, adenosine, α,β‐methylene ATP and 2‐methylthio ATP, appeared to be ineffective. 3 Under Ca 2+ ‐free conditions, the basal level of Ins(1,4,5)P 3 was lower than in the presence of Ca 2+ , and the ATP‐ and UTP‐induced formation of Ins(1,4,5)P 3 was diminished. 4 The Ins(1,4,5)P 3 formation induced by optimal ATP and UTP concentrations was not additive. ATP‐ and UTP‐induced Ins(1,4,5)P 3 formation showed cross‐desensitization, whereas cross‐desensitization was absent in responses elicited by one of the nucleotides and bradykinin. 5 The change in Ins(1,4,5)P 3 content induced by effective nucleotides was inhibited by suramin. Schild plots for suramin inhibition of Ins(1,4,5)P 3 formation in ATP‐ and UTP‐stimulated myotubes showed slopes greater than unity (1.63 ± 0.09 and 1.37 ± 0.11, respectively). Apparent pA 2 values were 4.50 ± 0.48 and 4.41 ± 0.63 for ATP and UTP, respectively. 6 Stimulation of the cells with ATP or UTP induced a rapid increase in intracellular Ca 2+ , followed by a slow decline to basal levels. Ca 2+ responses reached lower maximal values and did not show the slow phase in the absence of extracellular Ca 2+ . The ATP and UTP‐evoked increase in intracellular Ca 2+ was not additive and showed cross‐desensitization. Cross‐desensitization was absent in myotubes stimulated with one of the nucleotides and bradykinin. 7 These results show that ATP‐ and UTP‐induced formation of Ins(1,4,5)P 3 , Ca 2+ release from internal stores and Ca 2+ ‐influx from the extracellular space are mediated exclusively via the nucleotide type P 2 ‐purinoceptor in mouse C2C12 myotubes.