Objective   To observe the spontaneous Ca

2+

transients of interstitial cells of cajal (ICCs) and explore its mechanism in the rat bladder.    Methods   Single layer of smooth muscle bundles attached to the serosal layer of rat bladder were prepared and superfused with warmed physiological saline (PSS) to recover and maintain their activity. After spontaneous muscle movements of the muscle layers were visually detected

the tissues were loaded wi

th the fluo-4 AM and then spontaneous Ca

2+

transients of ICCs in the muscle layers were observed with laser scanning confocal microscopy. Nimodipine

2-aminoethoxydiphenylborate (2-APB)

ryanodine

thapsigargin

Ca

2+

free PSS and high Ca

2+

PSS were then used to investigate the mechanisms of spontaneous Ca

2+

transients in ICCs.    Results   Spontaneous Ca

2+

transients of smooth muscle cells (SMCs) and ICCs in the smooth layers were successfully detected. Nimodipine suppressed significantly Ca

2+

transients in SMCs but not in ICCs. Spontaneous Ca

2+

transients of ICCs were completely abolished by 2-aminoethoxydiphenylborate (2-APB)

ryanodine

thapsigargin

Ca

2+

free PSS and partly increased by high Ca

2+

PSS.    Conclusion   These results suggest that spontaneous Ca

2+

transients of ICCs rely on both Ca

2+

release from intracellular Ca

2+

stores and extracellular Ca

2+

entry through non L type Ca

2+

channels.