Ca2+ mobilization and activation of extracellular acidification by carbachol in acutely dispersed cells from guinea pig detrusor: Fura 2 fluorometry and microphysiometry using the cytosensor.

The study aim was to develop a simple in vitro model for pharmacophysiologi cal investigation of urinary bladder smooth muscles. Smooth muscle cells fr om guinea pig detrusor were dissociated, and the suspended cells were stimu lated with carbachol (CCh), an acetylcholine receptor agonist. Cytosolic Ca 2+ levels were determined using Fura 2 fluorescence and extracellular acidi fication rates were monitored by the Cytosensor microphysiometer. CCh dose- dependently increased cytosolic Ca2+ levels and extracellular acidification rates, with EC50 values of approximately 1 mu M. Both the acetylcholine mu scarinic receptor antagonist atropine and the M-3 muscarinic receptor-prefe rring antagonist 4-diphenylacetoxy-N-methylpiperidine (4-DAMP) inhibited th e effects of CCh, three orders of magnitude more potently than the selectiv e M-2 muscarinic receptor antagonist, methoctramine. These data indicate th e dominant role of M-3 receptors in guinea-pig bladder but fail to show cle ar evidence of any functional role for M-2 receptors. Since this finding ag rees with a number of other studies using in vivo and in vitro models (1), cell suspensions such as these may prove to be simple tools for the pharmac ological study of urinary bladder smooth muscle tissue.