Electrical slow waves in the small intestine are generated by pacemaker cells called interstitial cells of Cajal. Drumm et al. record clusters of Ca2+ transients in these cells that are entrained by voltage-dependent Ca2+ entry and which define the duration of the electrical slow waves.

All tissues were perfused and maintained with KRB solution containing (mmol/liter): 120.35 NaCl, 15.5 NaHCO 3 , 5.9 KCl, 1.2 MgCl 2 , 1.2 NaH 2 PO 4 , 2.5 CaCl 2 , and 11.5 glucose. The KRB solution warmed to a physiological temperature of 37 ± 0.2°C and bubbled with a mixture of 97% O 2 -3% CO 2 . For experiments using external solutions with zero [Ca 2+ ] o , CaCl 2 was omitted and 1 mM EGTA was added to the solution. NNC 55-0396 and TTA-A2 were purchased from Alomone Labs, nicardipine was purchased from Sigma-Aldrich, thapsigargin, isradipine, and ryanodine were purchased from Tocris Bioscience, and multiple batches of Xestospongin C (XeC) were purchased from Cayman Chemical.All versions of this article have been corrected. Correction