A role for Q type Ca2+ channels in neurotransmission in the rat urinary bladder

Abstract

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 ω‐conotoxin‐GVIA (300 nM) and ω‐agatoxin‐IVA (100 nM) respectively. The resistant portion (non‐N, non‐P) was sensitive to ω‐conotoxin‐MVIIC (3 μM), which in addition to N and P also blocks Q type channels at this concentration. ω‐Conotoxin‐MVIIC administered alone, inhibited the neurogenic response to the same degree as that observed in the combined presence of ω‐agatoxin‐IVA, ωconotoxin‐GVIA and ω‐conotoxin‐MVIIC. ω‐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 ω‐conotoxin‐GVIA (300 μM), ω‐agatoxin‐IVA (3 μM) (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 ω‐conotoxin‐MVIIC alone. Results suggest that neurotransmission in rat urinary bladder is supported by both N and Q type Ca2+ channels. 1995 British Pharmacological Society