EN
Although spontaneous phasic activity of detrusor muscle plays an important role in urinary bladder function there is little information regarding myogenic [Ca2+]i signals in this tissue. We have studied spontaneous, unstimulated [Ca2+]i signals in fura-2 loaded detrusor cells isolated from newborn (10-13 days old) guinea-pig urinary bladder. In newborn guinea pigs 35% of studied muscle cells displayed spontaneous [Ca2+]i oscillations with several kinetic patterns (from irregular to highly paced cycles). The oscillations were inhibited by external Ca2+ removal, treatment with L- and T-type Ca2+ channel blockers and by the hyperpolarizing drug pinacidil. Ca2+ stores were necessary to maintain oscillations, as indicated by the inhibitory effects of thapsigargin, ryanodine and 2-APB. Oscillations were also inhibited by folimycin, an inhibitor of acidic Ca2+ stores. Treatment with the selective inhibitors iberiotoxin and NPPB indicated that the oscillatory signal is also modulated by Ca2+ -activated K+ channels (inhibitory) and Ca2+ -activated Cl- channels (stimulatory). Our results indicate that detrusor cells from newborn guinea-pigs develop spontaneous [Ca2+]i oscillations due to Ca2+ influx through T- and L-type Ca2+ channels modulated by intracellular stores, including acidic pools. This activity could underlie the myogenic activity of urinary bladder during early stages of development.