Ca(2+) sparks and BK currents in gallbladder myocytes: role in CCK-induced response.
We sought to elucidate the regulation of gallbladder smooth muscle (GBSM) excitability by localized Ca(2+) release events (sparks) and large-conductance Ca(2+)-dependent (BK) channels by determining whether sparks exist in GBSM and, if so, whether they activate BK channels. Sparks were identified in isolated GBSM loaded with fluo 4. Each spark was associated with a transient outward current, suggesting communication of ryanodine receptor (RyR) channels with BK channels. This was confirmed by the inhibition of outward currents with iberiotoxin (100 nM), thapsigargin (200 nM), and ryanodine (10 microM). In current clamp mode, the transient BK currents were associated with brief membrane hyperpolarizations (10.9 +/- 1.3 mV). Because transient BK currents could dampen GBSM excitability, we tested whether CCK attenuates these events. CCK (10 nM) reduced the amplitude and frequency of transient BK currents, and subsequent caffeine application restored transient BK current activity. These results support the concept that RyRs and BK channels contribute to the regulation of GBSM excitability and that CCK can act in part by inhibiting this pathway.
Pozo
María J
MJ
Department of Physiology, University of Extremadura, 10071 Cáceres, Spain.
Pérez
Guillermo J
GJ
Nelson
Mark T
MT
Mawe
Gary M
GM
D000814:Aniline Compounds; D000818:Animals; D001896:Boron Compounds / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002766:Cholecystokinin / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes; D005704:Gallbladder / Q000166:cytology / Q000378:metabolism*; D006168:Guinea Pigs; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology; D014966:Xanthenes
D000814:Aniline Compounds; D001896:Boron Compounds; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D004791:Enzyme Inhibitors; C409648:Fluo 4; D005456:Fluorescent Dyes; D051036:Large-Conductance Calcium-Activated Potassium Channels; D010455:Peptides; D010726:Phosphodiesterase Inhibitors; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D019837:Ryanodine Receptor Calcium Release Channel; D014966:Xanthenes; D012433:Ryanodine; D002110:Caffeine; D019284:Thapsigargin; C064719:iberiotoxin; D002766:Cholecystokinin; C109986:2-aminoethoxydiphenyl borate; D009543:Nifedipine; D011188:Potassium; D002118:Calcium