<jats:sec><jats:title>Background and purpose:</jats:title><jats:p>Effects of imatinib mesylate, a Kit receptor tyrosine kinase inhibitor, on spontaneous activity of interstitial cells of <jats:italic>Cajal</jats:italic> (ICC) and smooth muscles in the stomach were investigated.</jats:p></jats:sec><jats:sec><jats:title>Experimental approach:</jats:title><jats:p>Effects of imatinib on spontaneous electrical and mechanical activity were investigated by measuring changes in the membrane potential and tension recorded from smooth muscles of the guinea‐pig stomach. Its effects on spontaneous changes in intracellular concentration of Ca<jats:sup>2+</jats:sup> ([Ca<jats:sup>2+</jats:sup>]<jats:sub>i</jats:sub>) (Ca<jats:sup>2+</jats:sup> transients) were also examined in fura‐2‐loaded preparations.</jats:p></jats:sec><jats:sec><jats:title>Key results:</jats:title><jats:p>Imatinib (1–10 μ<jats:sc>M</jats:sc>) suppressed spontaneous contractions and Ca<jats:sup>2+</jats:sup> transients. Simultaneous recordings of electrical and mechanical activity demonstrated that imatinib (1 μ<jats:sc>M</jats:sc>) reduced the amplitude of spontaneous contractions without suppressing corresponding slow waves. In the presence of nifedipine (1 μ<jats:sc>M</jats:sc>), imatinib (10 μ<jats:sc>M</jats:sc>) reduced the duration of slow waves and follower potentials in the antrum and accelerated their generation, but had little affect on their amplitude. In contrast, imatinib reduced the amplitude of antral slow potentials and slow waves in the corpus.</jats:p></jats:sec><jats:sec><jats:title>Conclusions and implications:</jats:title><jats:p>Imatinib may suppress spontaneous contractions of gastric smooth muscles by inhibiting pathways that increase [Ca<jats:sup>2+</jats:sup>]<jats:sub>i</jats:sub> in smooth muscles rather than by specifically inhibiting the activity of ICC. A high concentration of imatinib (10 μ<jats:sc>M</jats:sc>) reduced the duration of slow waves or follower potentials in the antrum, which reflect activity of ICC distributed in the myenteric layers (ICC‐MY), and suppressed antral slow potentials or corporal slow waves, which reflect activity of ICC within the muscle bundles (ICC‐IM), presumably by inhibiting intracellular Ca<jats:sup>2+</jats:sup> handling.</jats:p><jats:p><jats:italic>British Journal of Pharmacology</jats:italic> (2008) <jats:bold>154</jats:bold>, 451–459; doi:<jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" xlink:href="10.1038/bjp.2008.91">10.1038/bjp.2008.91</jats:ext-link>; published online 14 April 2008</jats:p></jats:sec>