A ROLE FOR Q-TYPE CA2+ CHANNELS IN NEUROTRANSMISSION IN THE RAT URINARY-BLADDER

1 In isolated bladder strips of the rat, a substantial component (46%) of the Ca2+-dependent contractile response to electrical field stimulation (5 Hz) was resistant to combined block of both N and P type Ca2+ channels by omega-conotoxin-GVIA (300 nM) and omega-agatoxin-IVA (100 nM) respectively. 2 The resistant portion (non-N, non-P) was sensitive to omega-conotoxin-MVIIC (3 mu M), which in addition to N and P also blocks Q type channels at this concentration. omega-Conotoxin-MVIIC administered alone, inhibited the neurogenic response to the same degree as that observed in the combined presence of omega-agatoxin-IVA, omega-conotoxin-GVIA and omega-conotoxin-MVIIC. 3 omega-Agatoxin-IVA (100 nM), a concentration that fully inhibits P type channels, had a negligible effect on the neurogenic response. Following blockade of N type Ca2+ channels with omega-conotoxin-GVIA (300 nM), omega-agatoxin-IVA (3 mu M) (a concentration well above that used to block P channels, inhibits Q type channels, but spares N type channels), inhibited the residual response to the same degree as omega-conotoxin-MVIIC alone. 4 Results suggest that neurotransmission in rat urinary bladder is supported by both N and Q type Ca2+ channels.