Suppression of the autooscillatory contractile activity of Physarum polycephalum plasmodium by the inhibitor of the IP3-Induced Ca2+ release, 2-aminoethoxydiphenyl borate

Abstract

In order to elucidate the function of inositol 1,4,5-trisphosphate (IP3)-activated reticular Ca2+ channel (IP3R) in autooscillatory contractile activity of Physarum polycephalum plasmodium, we applied 2-aminoethoxydiphenyl borate (2-APB), a membrane-permeable inhibitor of IP3-induced Ca2+ release. Taking into account that for the type 1 IP3 R the inhibitory efficacy of 2-APB decreases with the rise of the IP3 level [Bilmen, J.G. and Michelangeli, F., Cell Signal., 2002, vol. 14, no. 11, pp. 955–960], 2-APB was applied to plasmodium in normal conditions and after the treatment with glucose or 3-O-methylglucose, the attractants capable to induce an elevation of the IP3 production. We found that 20–50 μM 2-APB induced a reversible cessation of contractile autooscillations, which occurred in two different modes: as a fast stop and a gradual damping. The damping of oscillations was accompanied by an increase in their period, a prolongation of the contraction phase, and, often, by an increase in the mean level of the contraction force. The number of species responding by the fast stop at a 2-APB concentration of 50 μM was two times greater than at 20 μM 2-APB. In the presence of the attractants in concentrations of 10 and 50 mM, the fast stop was never observed at 20 μM of 2-APB. Moreover, the damping of oscillations was preceded by a period of varying duration, when the regular oscillatory mode was maintained. We conclude that the fast stop results from the direct inter-action of 2-APB with IP3R of Physarum polycephalum plasmodium and that IP3R is indispensable for the plasmodial oscillator.