Various Ca2+ -sensitive channels. Repeat determinations show stable responses in time controls. Increasing Ca2+ influx during neuronal activation by elevating bath Ca2+ concentration from baseline (2 mM) to 8.0 mM get CI-1011 decreased maximal GW 4064 web following frequency. Activation of SK and IK subtypes of Ca2+ -activated K+ channels with NS309 (5 M) also decreased following frequency. Activation of the BK subtype of Ca2+ -activated K+ channels with NS1619 (10 M) had no effect on following frequency. Blockade of Ca2+ -activated Cl- channels with niflumic acid (Nif A; 100 M) decreased following frequency. Blockade of the HCN channels with ZD7288 (10 M) had no effect. Bars show mean ?SEM. Significance testing was done by Student’s t test before converting to percentage change, P < 0.05, P < 0.01; numbers in the bar are n.C2012 The Authors. The Journal of PhysiologyC2012 The Physiological SocietyG. Gemes and othersJ Physiol 591.following frequency (P = 0.0015, n = 294). The weakness of this influence (R2 = 0.03) indicates that the T-junction is regulated by additional factors other than those that control axonal CV.Ca2+ -activated channels regulate propagation through the T-junctionproduce the depolarizing H-type current. These channels may augment the AHP (Maccaferri McBain, 1996), are activated by cytoplasmic Ca2+ (Schwindt et al. 1992; Pan, 2003), and regulate sensory neuron excitability (Hogan Poroli, 2008). However, blockade with ZD7288 (10 M) resulted in no change in following frequency (Fig. 5C). Together, these pharmacological observations indicate that propagation of APs through the T-junction is sensitive to regulation by Ca2+ -activated IK/SK and Cl- channels.We have previously shown that trains of APs similar to those used in the present recordings substantially elevate cytoplasmic Ca2+ in adult sensory neurons in intact DRGs (Gemes et al. 2010), while others have identified the critical role of cytoplasmic Ca2+ in regulating conduction through the T-junction in embryonic rat DRGs (Luscher et al. 1994a, 1996). We tested whether cytoplasmic Ca2+ regulates AP propagation in our model of adult DRGs by elevating the Ca2+ concentration in the bath solution, which increases cytoplasmic Ca2+ accumulation during sensory neuron activation (Fuchs et al. 2007; Lirk et al. 2008). Whereas time control recordings showed no effect (Fig. 5C), elevating bath Ca2+ by switching from aCSF containing 2 mM Ca2+ to one containing 8 mM Ca2+ (in a separate experiment) decreased the following frequency (Fig. 5C), which is consistent with a sensitivity of T-junction propagation to cytoplasmic Ca2+ concentration. Possible molecular sites of action of cytoplasmic Ca2+ include Ca2+ -dependent membrane channels. Sensory neurons express Ca2+ -activated K+ (KCa) channels with pharmacological features of large, intermediate and small conductance (BK, IK and SK) subtypes (Sarantopoulos et al. 2003), which respectively contribute to the early, intermediate and late phases of the AHP. We tested the role of KCa channels on T-junction conduction by determining the following frequency in sensory neurons before and after pharmacological activation of these channels. NS309 (5 M), which increases current through the IK and SK channels (Pedarzani et al. 2005; Strobaek et al. 2006), decreased following frequency (Fig. 5C) and concurrently expanded the somatic AHParea following the train (baseline: 1760 ?4733 ms mV; NS309: 5799 ?1464 ms mV; P < 0.01). However, NS1619 (10 M), which sele.Various Ca2+ -sensitive channels. Repeat determinations show stable responses in time controls. Increasing Ca2+ influx during neuronal activation by elevating bath Ca2+ concentration from baseline (2 mM) to 8.0 mM decreased maximal following frequency. Activation of SK and IK subtypes of Ca2+ -activated K+ channels with NS309 (5 M) also decreased following frequency. Activation of the BK subtype of Ca2+ -activated K+ channels with NS1619 (10 M) had no effect on following frequency. Blockade of Ca2+ -activated Cl- channels with niflumic acid (Nif A; 100 M) decreased following frequency. Blockade of the HCN channels with ZD7288 (10 M) had no effect. Bars show mean ?SEM. Significance testing was done by Student's t test before converting to percentage change, P < 0.05, P < 0.01; numbers in the bar are n.C2012 The Authors. The Journal of PhysiologyC2012 The Physiological SocietyG. Gemes and othersJ Physiol 591.following frequency (P = 0.0015, n = 294). The weakness of this influence (R2 = 0.03) indicates that the T-junction is regulated by additional factors other than those that control axonal CV.Ca2+ -activated channels regulate propagation through the T-junctionproduce the depolarizing H-type current. These channels may augment the AHP (Maccaferri McBain, 1996), are activated by cytoplasmic Ca2+ (Schwindt et al. 1992; Pan, 2003), and regulate sensory neuron excitability (Hogan Poroli, 2008). However, blockade with ZD7288 (10 M) resulted in no change in following frequency (Fig. 5C). Together, these pharmacological observations indicate that propagation of APs through the T-junction is sensitive to regulation by Ca2+ -activated IK/SK and Cl- channels.We have previously shown that trains of APs similar to those used in the present recordings substantially elevate cytoplasmic Ca2+ in adult sensory neurons in intact DRGs (Gemes et al. 2010), while others have identified the critical role of cytoplasmic Ca2+ in regulating conduction through the T-junction in embryonic rat DRGs (Luscher et al. 1994a, 1996). We tested whether cytoplasmic Ca2+ regulates AP propagation in our model of adult DRGs by elevating the Ca2+ concentration in the bath solution, which increases cytoplasmic Ca2+ accumulation during sensory neuron activation (Fuchs et al. 2007; Lirk et al. 2008). Whereas time control recordings showed no effect (Fig. 5C), elevating bath Ca2+ by switching from aCSF containing 2 mM Ca2+ to one containing 8 mM Ca2+ (in a separate experiment) decreased the following frequency (Fig. 5C), which is consistent with a sensitivity of T-junction propagation to cytoplasmic Ca2+ concentration. Possible molecular sites of action of cytoplasmic Ca2+ include Ca2+ -dependent membrane channels. Sensory neurons express Ca2+ -activated K+ (KCa) channels with pharmacological features of large, intermediate and small conductance (BK, IK and SK) subtypes (Sarantopoulos et al. 2003), which respectively contribute to the early, intermediate and late phases of the AHP. We tested the role of KCa channels on T-junction conduction by determining the following frequency in sensory neurons before and after pharmacological activation of these channels. NS309 (5 M), which increases current through the IK and SK channels (Pedarzani et al. 2005; Strobaek et al. 2006), decreased following frequency (Fig. 5C) and concurrently expanded the somatic AHParea following the train (baseline: 1760 ?4733 ms mV; NS309: 5799 ?1464 ms mV; P < 0.01). However, NS1619 (10 M), which sele.
