K+-stimulation of the phosphoinositide pathway in guinea-pig ileum longitudinal smooth muscle is predominantly neuronal in origin and mediated by the entry of extracellular Ca2+

S. P. Watson, J. Lai, T. Sasaguri

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K+ and scorpion toxin stimulate formation of inositol phosphates in guinea-pig ileum longitudinal smooth muscle slices. The response to these two agents is not additive. The response to K+ is inhibited partially by nifedipine and partially by ω-conotoxin. When given together the effect of these two Ca2+ channel blockers is additive and the response of K+ is reduced by more than 80%. The response to scorpion toxin is inhibited completely by tetrodotoxin, partially by ω-conotoxin but not by atropine or nifedipine. Scorpion toxin induces a similar formation of inositol phosphates in collagenase-dispersed cells to that seen in cross-chopped slices. The responses to scorpion toxin and K+ are inhibited completely when the extracellular Ca2+ concentration is reduced to below cytosolic levels (<100 nM). Neither nifedipine nor ω-conotoxin, either alone or in combination, inhibited formation of inositol phosphates by substance P or carbachol. Both of these agonists induced a significant formation of inositol phosphates even when the extracellular Ca2+ concentration was reduced to 10 nM. These results indicate that K+ and scorpion toxin induce formation of inositol phosphates through the mobilisation of extracellular Ca2+. The response to K+ appears to occur predominantly in neuronal cells.

Original languageEnglish
Pages (from-to)212-216
Number of pages5
JournalBritish Journal of Pharmacology
Issue number1
Publication statusPublished - Jan 1 1990
Externally publishedYes


All Science Journal Classification (ASJC) codes

  • Pharmacology

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