MULTIPLE SUBTYPES OF VOLTAGE-GATED CALCIUM-CHANNEL MEDIATE TRANSMITTER RELEASE FROM PARASYMPATHETIC NEURONS IN THE MOUSE BLADDER

Multiple subtypes of voltage-gated calcium channels are coupled to tra nsmitter release from central neurons; however, only N-type channels h ave been shown to play a role in autonomic neurons, The aim of the pre sent study was to investigate potential roles for other channel subtyp es in transmitter release from parasympathetic neurons in the mouse bl adder using calcium channel toxins alone and in combination, Transmitt er release was measured indirectly by recording the contraction of bla dder dome strips in response to electrical stimulation of the neurons by single pulses or trains of 20 pulses at 1-50 Hz. omega-Conotoxin-GV IA (GVIA) and omega-conotoxin-MVIIC (MVIIC) inhibited contractions in a concentration-dependent manner, with IC50 values of similar to 30 an d 200 nM, respectively, at low stimulation frequencies. omega-Agatoxin -IVA (agatoxin) alone did not have any significant effect up to 300 nM . Cumulative addition of the toxins demonstrated that 300 nM agatoxin had a significant effect after N-type channels were blocked with 100 n M GVIA, MVIIC (3 mu M) reduced the contraction amplitude further. Test ing the toxins on the cholinergic or purinergic component of the contr action separately showed that acetylcholine release depends primarily on N-type channels and, to a lesser extent, on P- and Q-type channels, whereas ATP release involves predominantly P- and Q-type channels, In conclusion, parasympathetic neurons in the mouse bladder, like centra l neurons, use multiple calcium channel subtypes, Furthermore, the rel ease of the two main transmitters in these neurons has differing depen dencies on the calcium channel subtypes.