Abstract
Intracellular Ca 2+ waves and spontaneous transient depolarizations were investigated in gallbladder smooth muscle (GBSM) whole mount preparations with intact mucosal layer [full thickness (FT)] by laser confocal imaging of intracellular Ca 2+ and voltage recordings with microelectrodes, respectively. Spontaneous Ca 2+ waves arose most often near the center, but sometimes from the extremities, of GBSM cells. They propagated regeneratively by Ca 2+ -induced Ca 2+ release involving inositol 1,4,5-trisphosphate [Ins( 1 , 4 , 5 )P 3 ] receptors and were not affected by TTX and atropine (ATS). Spontaneous Ca 2+ waves and spontaneous transient depolarizations were more prevalent in FT than in isolated muscularis layer preparations and occurred with similar pattern in GBSM bundles. Ca 2+ waves were abolished by the Ins( 1 , 4 , 5 )P 3 receptor inhibitors 2-aminoethoxydiphenyl borate and xestospongin C and by caffeine and cyclopiazonic acid. These events were reduced by voltage-dependent calcium channels (VDCCs) inhibitors diltiazem and nifedipine, by PLC inhibitor U-73122, and by thapsigargin and ryanodine. ACh, CCK, and carbachol augmented Ca 2+ waves and induced Ca 2+ flashes. The actions of these agonists were inhibited by U-73122. These results indicate that in GBSM, discharge and propagation of Ca 2+ waves depend on sarco(endo)plasmic reticulum (SR) Ca 2+ release via Ins( 1 , 4 , 5 )P 3 receptors, PLC activity, Ca 2+ influx via VDCCs, and SR Ca 2+ concentration. Neurohormonal enhancement of GBSM excitability involves PLC-dependent augmentation and synchronization of SR Ca 2+ release via Ins( 1 , 4 , 5 )P 3 receptors. Ca 2+ waves likely reflect the activity of a fundamental unit of spontaneous activity and play an important role in the excitability of GBSM.