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 (DeltaF/F0) and 2.75 +/- 0.17 cycles/min to 0.02 +/- 0.01 (DeltaF/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 (DeltaF/F0) and 2.27 +/- 0.18 cycles/min to 0.43 +/- 0.03 (DeltaF/F0) and 2.87 +/- 0.07 cycles/min. 2-Aminoethoxydiphenyl borane (2-APB), an IP(3) 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 IP(3)-induced calcium release signaling pathway.

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