Capacitative calcium entry in guinea pig gallbladder smooth muscle in vitro.
This study investigates the involvement of capacitative Ca2+ entry in excitation-contraction coupling in guinea pig gallbladder smooth muscle. Thapsigargin (0.1 nM-1 microM, a sarcoplasmic reticulum Ca(2+)-ATPase inhibitor) produced slowly developing sustained tonic contractions in guinea pig isolated gallbladder strips. All contractions approached 50% of the response to carbachol (10 microM) after 55 min. Contractile responses to thapsigargin (1 microM) were abolished in a Ca(2+)-free medium. Subsequent re-addition of Ca2+ (2.5 mM) produced a sustained tonic contraction (99 +/- 6% of the carbachol response). The contractile response to Ca2+ re-addition following incubation of tissues in a Ca(2+)-free bathing solution in the absence of thapsigargin was significantly less than in its presence (79 +/- 4 % vs 100 +/- 7 % of carbachol; p < 0.05). Contractile responses to Ca2+ re-addition following treatment with thapsigargin were attenuated by (a) the L-type voltage-operated Ca2+ channel antagonist, nifedipine (10 microM) and (b) the general inhibitor of Ca2+ entry channels including store-operated channels, SK&F96365 (50 microM and 100 microM). In separate experiments, responses to Ca2+ re-addition were essentially abolished by the tyrosine kinase inhibitor, genistein (100 microM). These results suggest that capacitative Ca2+ entry provides a source of activator Ca2+ for guinea pig gallbladder smooth muscle contraction. Contractile responses to Ca2+ re-addition following depletion of sarcoplasmic reticulum Ca2+ stores with thapsigargin, are mediated in part by Ca2+ entry through voltage-operated Ca2+ channels and by capacitative Ca2+ entry through store-operated Ca2+ channels which can be blocked by SK&F96365. Furthermore, capacitative Ca2+ entry in this tissue may be modulated by tyrosine kinase.
Quinn
T
T
Department of Veterinary Physiology and Biochemistry, Faculty of Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland.
Molloy
M
M
Smyth
A
A
Baird
A W
AW
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005704:Gallbladder / Q000033:anatomy & histology / Q000502:physiology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000502:physiology*; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D018679:Cholinergic Agonists; D004791:Enzyme Inhibitors; D019284:Thapsigargin; D002217:Carbachol; D009543:Nifedipine; D002118:Calcium