Inhibitors of spasmogen-induced Ca2+ channel suppression in smooth muscle cells from small intestine.
1. Whole-cell patch-clamp recordings were made from smooth muscle cells isolated from the longitudinal muscle layer of guinea-pig ileum. Carbachol (acting at muscarinic receptors) or histamine (acting at H1 histamine receptors) suppressed Ca2+ channel current. The effect of either agonist had an initial transient component followed by a sustained component. 2. Wortmannin inhibited transient and sustained components of carbachol-induced Ca2+ channel current suppression: half-effective inhibitory concentrations (IC50) were 1.1 microM and 0.6 microM for the two components respectively. Wortmannin also inhibited the transient phase of carbachol-induced cationic current (IC50 1.6 microM) and Ca2+-dependent K+-current (IC50 1.7 microM). Wortmannin did not appear to produce any direct block of cationic channels or Ca2+ channels. 3. Intracellular application of the phospholipase inhibitor D609 (tricyclodecan-9-ylxanthogenate) inhibited transient and sustained components of histamine action on the Ca2+ channel current: the IC50 was about 130 microM for both components. Carbachol action on Ca2+ channels was also inhibited by D609. D609 had no significant direct blocking effect on Ca2+ channels, cationic channels activated by carbachol, or Ca2+-activated K+-current in response to flash-photolysis of caged-inositol 1,4,5-trisphosphate. 4. Micromolar concentrations of wortmannin and D609 are inhibitors of both components of spasmogen-induced Ca2+ channel suppression. The data suggest that both components are mediated by a common, or similar, signal transduction element which is a phospholipase C (PLC) or phospholipase D (PLD) isoform.
Unno
T
T
Department of Veterinary Science, Faculty of Agriculture, Gifu University, Japan.
Beech
D J
DJ
Komori
S
S
Ohashi
H
H
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002217:Carbachol / Q000494:pharmacology*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D006168:Guinea Pigs; D006632:Histamine / Q000494:pharmacology*; D007421:Intestine, Small / Q000187:drug effects; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D011968:Receptors, Histamine / Q000187:drug effects; D011976:Receptors, Muscarinic / Q000187:drug effects; D013997:Time Factors
D002121:Calcium Channel Blockers; D011968:Receptors, Histamine; D011976:Receptors, Muscarinic; D006632:Histamine; D002217:Carbachol