Abstract
Electrical pacemaker activity generates phasic contractions and motility patterns such as segmentation and peristalsis in the gastrointestinal tract. Pacemaker currents are generated in interstitial cells of Cajal (ICC), which release Ca(2+) from intracellular stores that stimulates Ca(2+)-activated Cl(-) channels (CaCCs) in the plasma membrane. Thus, Ca(2+) stores must be maintained to sustain pacemaker activity. Store-operated Ca(2+) entry (SOCE) facilitates the refilling of Ca(2+) stores by a mechanism dependent upon interactions between STIM and Orai proteins. We investigated the role of SOCE in ICC pacemaker activity. Reintroduction of extracellular Ca(2+) in store-depleted ICC resulted in CaCC activation. Blocking CaCCs revealed an inwardly rectifying current with properties of a Ca(2+) release-activated current (I(CRAC)). An inhibitory peptide that interfered with the STIM-Orai interaction blocked I(CRAC) in HEK 293 cells expressing STIM1 and Orai1 and blocked spontaneous transient inward currents (STICs) and slow wave currents in ICC. STICs, which are fundamental pacemaker events in ICC, were blocked by an Orai antagonist. Imaging of Ca(2+) transients linked to pacemaker activity in ICC in intact muscles showed that the Orai antagonist blocked Ca(2+) transients in ICC. These data suggest that Ca(2+) recovery through STIM-Orai interactions is necessary to maintain ICC pacemaker activity.