The centenary of the problem of the interstitial cells of Cajal.

The intestinal pacemaker cells are often confused with the interstitial cells of Cajal. However, under this term, at least three kinds of histological structures have been discussed: 1) fibroblasts, 2) fibroblast-like cells consisting of several subclasses, and 3) specialized smooth muscle cells. To our surprise, Cajal (1889, 1893) described a chimeric composition of glial (Schwann) cells and varicose nerve terminals as interstitial (nerve) cells. Cajal could not explain the net work formation of the autonomic periphery by the neuron doctrine. Therefore, he described it as special neuron system. We studied a unique smooth muscle tissue that produces regular mechanical contractions of 10-12 cycles/min at the mesenteric border of the pacemaker area in the guinea-pig colonic flexure region. Based on the results of our studies, we reevaluated both Cajal's original description and the cellular identity of intestinal pacemakers.