Actin Microfilament Involved in Regulation of Pacemaking Activity in Cultured Interstitial Cells of Cajal from Murine Intestine

The present study investigated the effect of actin microfilament structure on pacemaker currents and calcium oscillation in cultured murine intestinal interstitial cells of Cajal (ICCs) by whole-cell patch-clamp technique and calcium imaging technique. Cytochalasin B, a disruptor of actin microfilaments, decreased the amplitude and frequency of pacemaker currents from 491.32 ± 160.33 pA and 11.73 ± 0.79 cycles/min to 233.12 ± 92.00 pA and 10.29 ± 0.76 cycles/min. Cytochalasin B also decreased the amplitude and frequency of calcium oscillation from 0.32 ± 0.08 (ΔF/F0) and 2.75 ± 0.17 cycles/min to 0.02 ± 0.01 (ΔF/F0) and 1.20 ± 0.08 cycles/min. Phalloidin, a stabilizer of actin microfilaments, increased the amplitude and frequency of pacemaker currents from 751.79 ± 282.82 pA and 13.93 ± 1.00 cycles/min to 1234.34 ± 607.83 pA and 14.68 ± 1.00 cycles/min. Phalloidin also increased the amplitude and frequency of calcium oscillation from 0.26 ± 0.01 (ΔF/F0) and 2.27 ± 0.18 cycles/min to 0.43 ± 0.03 (ΔF/F0) and 2.87 ± 0.07 cycles/min. 2-Aminoethoxydiphenyl borane (2-APB), an IP₃ receptor blocker, suppressed both pacemaker currents and calcium oscillations. 2-APB also blocked the phalloidin-induced increase in pacemaker currents and calcium oscillation. Ryanodine, an inhibitor of calcium-induced calcium release, did not affect pacemaker current but suppressed calcium oscillations. Ryanodine had no effect on altering phalloidin-induced increases in pacemaker current and calcium oscillation. These results suggest that actin microfilaments regulate pacemaker activity via the IP₃-induced calcium release signaling pathway.