Phospholipase C mediated Ca2+ signals in murine urinary bladder smooth muscle

Muscarinic stimulation of urinary bladder induces contraction via an increase in intracellular Ca2+ concentration that results from Ca2+ influx through Ca2+ channels and/or IP3-mediated Ca2+ release controlled by phospholipase C (PLC) signalling. The significance of PLC/IP3 signalling in this cascade has recently been questioned because PLC inhibitors were without effect on carbachol-induced contractions in detrusor muscle strips. However, PLC/IP3-mediated Ca2+ release was clearly observed in recordings of Ca2+ signals in isolated myocytes. Therefore, we investigated the presence of PLC/IP3-dependent Ca2+ release by directly monitoring Ca2+ signals in intact detrusor muscle strips. Concomitant Ca2+ signals from Ca2+ channel activity were eliminated by the Ca2+ channel antagonist isradipine (3 µM) or by the use of muscles from Cav1.2 channel-deficient (SMACKO) mice. In absence of Ca2+ channel activity, carbachol elicited contractions and Ca2+ signals in muscles from wild type and SMACKO mice that were inhibited by the PLC inhibitor U73122 (10 µM). The results show that PLC/IP3-dependent Ca2+ release is activated by stimulation with carbachol in urinary bladder smooth muscle but has a minor contribution to overall carbachol-induced Ca2+ signals.