Abstract
To investigate the possible contribution of T-type Ca channels to the generation of spontaneous electrical activity in detrusor smooth muscles of the guinea-pig, the effects of blockers for the channels on action potentials were examined using intracellular recording techniques. Isometric tension recording and intracelluar Ca measurement using furaPE3 loaded preparations were also carried out. Two types of action potentials were generated in detrusor smooth muscles of the guinea-pig bladder. Individual type of action potential is readily blocked by nefedipine(1μM) while bursting action potentials were converted into individual depolarizations. Higher concentrations of nifedipine(10-30μM) were required to block the depolarizations. Ni2+(100-300μM) changed individual action potential to bursts without changing either membrane potential or dV/dt of action potentials. Mibefradil(1μM), another T-type Ca channel blocker, also changed the pattern of action potential without affecting on their time courses. Consistently Ni2+ increase the amplitude of spontaneous contractions and Ca transients, and reduced their frequency. These result suggested that T-type Ca channel may determine the frequency of spontaneous action potential whereas their amplitude mostly depends on the activity of L-type Ca channel. [Jpn J Physiol 54 Suppl:S124 (2004)]
