Depletion of either ryanodine- or IP3-sensitive calcium stores activates capacitative calcium entry in mouse anococcygeus smooth muscle cells.
The properties of the calcium stores coupled to a depletion-operated cation current (IDOC) proposed to underlie capacitative calcium entry were studied in single smooth muscle cells isolated from the mouse anococcygeus using the whole-cell patch-clamp technique. Both caffeine (10 mM) and carbachol (50 microM) activated an initial, large ( approximately 200 pA), transient, calcium-dependent chloride current (IClCa) followed by a smaller ( approximately 10 pA) sustained, non-selective cation current (IDOC). Intracellular application of heparin (5 mg ml-1) abolished the response to carbachol but potentiated that to caffeine. Ryanodine (3 microM) activated IDOC but not IClCa; ryanodine (30 microM) failed to produce any response. Both concentrations of ryanodine abolished the response to caffeine and prevented activation of IClCa by carbachol. In the presence of 30 microM, but not 3 microM, ryanodine, carbachol was able to activate IDOC. Cyclopiazonic acid (CPA; 10 microM) abolished the response to carbachol; however, caffeine was still able to activate IClCa. In whole-muscle tension recordings, ryanodine at both 3 and 30 microM produced contractions of the tissue but only that in response to the lower concentration was maintained. Thus, depletion of either inositol 1,4, 5-trisphosphate-(IP3-) sensitive or ryanodine-sensitive calcium stores is able to activate IDOC, and, by extension, capacitative calcium entry in this tissue.
Wayman
C P
CP
Pharmacology Group, Division of Biomedical Sciences, King's College London, Manresa Road, London SW3 6LX, UK.
Gibson
A
A
McFadzean
I
I
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002217:Carbachol / Q000494:pharmacology; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D018118:Chloride Channels / Q000502:physiology; D004553:Electric Conductivity; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D008297:Male; D051379:Mice; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000378:metabolism*; D010277:Parasympathomimetics / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D012433:Ryanodine / Q000378:metabolism* / Q000494:pharmacology
D000697:Central Nervous System Stimulants; D018118:Chloride Channels; D004791:Enzyme Inhibitors; D007211:Indoles; D010277:Parasympathomimetics; D012433:Ryanodine; D002110:Caffeine; D015544:Inositol 1,4,5-Trisphosphate; D002217:Carbachol; D006493:Heparin; D000252:Calcium-Transporting ATPases; D002118:Calcium; C000543:cyclopiazonic acid