Retrograde and anterograde transport of horseradish peroxidase-wheat germ agglutinin (HRP-WGA) conjugate was used to study the organization of primary afferent neurons innervating the masticatory muscles. HRP applied to the nerves of jaw-closing muscles--the deep temporal (DT), masseter (Ma), and medial pterygoid (MP)--labeled cells in the trigeminal ganglion and the mesencephalic trigeminal nucleus (Vmes), whereas HRP applied to nerves of the jaw-opening muscles--anterior digastric (AD) and mylohyoid (My)--labeled cells only in the trigeminal ganglion. Cell bodies innervating the jaw-closing muscles were found with greater frequency in the intermediate region of the mandibular subdivision, while somata supplying the jaw-opening muscles were predominant posterolaterally. The distribution of their somatic sizes was unimodal and limited to a subpopulation of smaller cells. Projections of the muscle afferents of ganglionic origin to the trigeminal sensory nuclear complex (TSNC) were confined primarily to the caudal half of pars interpolaris (Vi), and the medullary and upper cervical dorsal horns. In the Vi, Ma, MP, AD, and My nerves terminated in the lateral-most part of the nucleus with an extensive overlap in projections, save for the DT nerve, which projected to the interstitial nucleus or paratrigeminal nucleus. In the medullary and upper cervical dorsal horns, the main terminal fields of individual branches were confined to laminae I/V, but the density of the terminals in lamina V was very sparse. The rostrocaudal extent of the terminal field in lamina I differed among the muscle afferents of origin, whereas in the mediolateral or dorsoventral axis, a remarkable overlap in projections was noted between or among muscle afferents. The terminals of DT afferents were most broadly extended from the rostral level of the pars caudalis to the C3 segment, whereas the MP nerve showed limited projection to the middle one-third of the pars caudalis. Terminal fields of the Ma, AD, and My nerves appeared in the caudal two-thirds of the pars caudalis including the first two cervical segments, the caudal half of the pars caudalis and the C1 segment, and in the caudal part of the pars caudalis including the rostral C1 segment, respectively. This rostrocaudal arrangement in the projections of muscle nerves, which corresponds to the anteroposterior length of the muscles and their positions, indicates that representation of the masticatory muscles in lamina I reflects an onion-skin organization. These results suggest that primary muscle afferent neurons of ganglionic origin primarily mediate muscle pain.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of Ca2+ release channels in the sarcoplasmic reticulum in modulating physiological automaticity of the sinoatrial (SA) node was studied by recording transmembrane action potentials and membrane ionic currents in small preparations of the rabbit SA node. Ryanodine, which modifies the conductance and gating behavior of the Ca2+ release channels, was used to block Ca2+ release from the sarcoplasmic reticulum. Superfusion of 1-mM ryanodine decreased the spontaneous firing frequency as well as the maximal rate of depolarization of the SA, and these reductions reached a steady state within approximately 5 min. The action potential recordings revealed that the latter part of diastolic depolarization was depressed and that the take-off potential became less negative. This suggested that the negative chronotropic effect of ryanodine resulted from the blockade of physiological Ca2+ release from the sarcoplasmic reticulum. In voltage clamp experiments, using double-microelectrode techniques, ryanodine did not markedly reduce the Ca2+ current (ICa) but decreased the delayed rectifying K+ current (IK), the steady-state inward current (Iss), and the hyperpolarization-activated inward current (Ih). These observations suggest that, even when the function of C2+ channels in the cell membrane is normally maintained, depression of Ca2+ release channels in the sarcoplasmic reticulum would prevent sufficient elevation of the Ca2+ concentration in SA node cells for the activation of various ionic currents, and, thus adversely affect the physiological automaticity of this primary cardiac pacemaker.

The rabbit A-V node was dissected into pieces (0.2 x 0.2 x 0.2 mm) smaller than its space constant of 692 +/- 96 micrometers (n = 5). These small specimens showed spontaneous action potentials whose configurations were similar to those of large specimens before dissection. The membrane time constant was 21.5 +/- 1.5 ms (n = 5). Voltage clamp experiments were performed on the above specimens using the two-microelectrode technique. On depolarization from the holding potential of -40 mV to various potential levels a transient inward current and delayed outward current were recorded. On repolarization an outward current tail was observed. The transient inward current was blocked by application of D 600 (2 x 10(-7) g/ml) but was insensitive to TTX (1 x 10(-7) g/ml). The inward current was decreased by superfusion with Na- or Ca-free Tyrode solution. Thus, this current was classified as the slow inward current (is). When the K concentration in the Tyrode solution was varied, the reversal potential of the outward current tail changed as expected for a K electrode, indicating that the outward current was carried by K ions. On hyperpolarization slow activation of inward current was recorded. The reversal potential of this current was between -20 and -30 mV, which was analogous to hyperpolarization activated current, ih, in the S-A node. A contribution of sodium current (iNa) to the action potential was obviously demonstrated from an inhibitory effect of TTX on the upstroke of the anodal break excitation. The ionic selectivity of each current system is compared with analogous current systems in other cardiac tissues and a possible mechanism for the slow conduction in the A-V node is discussed.

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1 Two types of Ca 2+ channel a 1 -subunits were co-expressed in Xenopus oocytes with the Ca 2+ channel a 2 -and b 1 -subunits. The Ba 2+ current through the a 1C a 2 b and the a 1B a 2 b channels had electrophysiological and pharmacological properties of L-and N-type Ca 2+ channels, respectively. 2 Amlodipine had a strong blocking action on both the L-type and N-type Ca 2+ channels expressed in the oocyte. The potency of the amlodipine block on the N-type Ca 2+ channel was comparable to that on the L-type Ca 2+ channel. At 7100 mV holding potential, the IC 50 values for amlodipine block on the L-type and N-type Ca 2+ channel were 2.4 and 5.8 mM, respectively. 3 The blocking action of amlodipine on the N-type Ca 2+ channel was dependent on holding potential and extracellular pH, as has been observed with amlodipine block on the L-type Ca 2+ channel. A depolarized holding potential and high pH enhanced the blocking action of amlodipine, 4 The time course of block development by amlodipine was similar for L-type and N-type Ca 2+ channels. However, it was slower than the time course of block development by nifedipine for the L-type Ca 2+ channel.