P-type Ca2+ channels mediate excitatory and inhibitory synaptic transmitter release in crayfish muscle.

Abstract

The toxin fraction (FIX) and peptide to-Aga-WA from the venom of the funnel-web spider Agelenopsis aperta, as well as a synthetic analogue ofFX, speciically block the P-type voltage-dependent Cam channel (VDCC). The effects of these toxins on synaptic transmission were studied in the neuromuscular synapses of the crayfish opener muscle, which has a single excitatory and a single inhibitory motoneuron. FIX selectively and reversibly blocked excitatory and inhibitory stsynaptic currents and potentials in a dosedependent manner. FIX had no effect on ( The crayfish opener neuromuscular system is a particularly well-suited preparation to define the type of VDCC involved in excitatory and inhibitory transmitter release in invertebrate neuromuscular synapses. Its distinguishing features are that opener muscle fibers are innervated by single excitatory and inhibitory axons that can be experimentally studied separately, and which release L-glutamate (Glu) and 't-aminobutyric acid (GABA) as transmitter, respectively (27,28 MATERIALS AND METHODSThe neuromuscular preparation of the opener muscle of the first walking leg of crayfish (Procambarus clarkii) was used (Fig. 1A). The muscle, which was separated at the propodite, and the nerve bundles, which include separate excitatory and inhibitory axons, were identified and isolated at the meropodite and transferred to a perfusion chamber (2 ml).

The Neuromuscular Junctions of the Slow and the Fast Excitatory Axon in the Closer of the CrabEriphia spinifronsAre Endowed with Different Ca2+Channel Types and Allow Neuron-Specific Modulation of Transmitter Release by Two Neuropeptides

“…The predominant role of P/Q-like channels in transmitter release observed in our study is in accord with results from crayfish and crab (Araque et al, 1994;Blundon et al, 1995;Wright et al, 1996;Hong and Lnenicka, 1997;Hurley and Graubard, 1998) and mammals, but in the rat, motor terminals at some muscles also contain a small fraction of N-type channels (Westenbroek et al, 1998). In frog and lizard neuromuscular synapses, N-or L-type channels mediate transmission (Lindgren and Moore, 1989;Katz et al, 1995;Arenson and Gill, 1996).…”

“…Although its physiological type was not stated, it is likely a fast-type neuron because of its high output terminals. Effects of -CgTX were not observed in recent studies of motor neurons in crustaceans (Araque et al, 1994;Wright et al, 1996;Hurley and Graubard, 1998). This led to the conclusion that N-like channels are not involved in neuromuscular transmission in crustaceans.…”

“…In crayfish, additional subtypes are present that are pharmacologically different from channels characterized in vertebrate neurons (Richmond et al, 1995(Richmond et al, , 1996Hong and Lnenicka, 1997). At crustacean neuromuscular junctions, transmitter release is thought to be mediated through P-type channels, with no contribution by N-, Q-, or L-type (Araque et al, 1994;Blundon et al, 1995;Wright et al, 1996;Hurley and Graubard, 1998).…”

“…There is evidence for L-, N-, P/Q-, or T-like channels in molluscs (for review, see Kits and Mansvelder, 1996), insects (for review, see Wicher et al, 2001), and crustaceans (Araque et al, 1994;Blundon et al, 1995;Chrachri, 1995;Wright et al, 1996;Hong and Lnenicka, 1997;Hurley and Graubard, 1998;GarciaColunga et al, 1999). In crayfish, additional subtypes are present that are pharmacologically different from channels characterized in vertebrate neurons (Richmond et al, 1995(Richmond et al, , 1996Hong and Lnenicka, 1997).…”

Synaptic structural complexity as a factor enhancing probability of calcium-mediated transmitter release

“…The calcium current-voltage relation, in voltageclamped terminals, has onset activation, peak, and reversal potentials of -35, -10, and calcium equilibrium potential (EC,) = +30 mV, respectively (Wright et al 1994). Funnel web spider toxin is the effective blocker in this preparation, as is the case for vertebrate P-type Ca, channels (Araque et al 1994;Usowicz et al 1992;Wright et al 1994). The distinctive properties of the P-type channel were initially defined in cerebellar Purkinje cells.…”