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.
|Number of pages||5|
|Journal||British Journal of Pharmacology|
|Publication status||Published - 1990|
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