In a recent study we investigated the interaction of 5-aminolaevulinic acid (5-ALA) and Bay K 8644 as a new approach for photodynamic therapy to induce apoptosis in cancer cells. After a treatment of several hours, smooth muscle tissue loses its contractility due to induction of apoptosis and calcium mismanagement.

Generally, gastric smooth muscle tissue consists of different interacting cell types (smooth muscle (SM), interstitial cells (Cajal-like; ICC) and nerve terminals (NT)). To answer, how these cell types are involved in the 5-ALA induced dysfunction, we applied an electrical field stimulation paradigm during the on-going process of apoptosis in varid controlled siuations. Short low-threshold pulses (1 ms) activate NT (inhibited by TTX); intermediate pulses (5 ms) activate NT and ICC; long pulses (10 ms) activate NT, ICC and SM. Phasic-rhythmic activity in gastric antrum (due to ICC activity) ceased during long-term treatment with 5-ALA and Bay K 8644. Nerve activity seemed insensitive to the drugs. With the pharmacological induction of light sensitivity the smooth muscle tone was altered time-dependently. We conclude, that both, the modulation of SM function and inhibitions of ICC are the targets for such pharmacological treatment.