Slack and Slick KNa channels are required for the depolarizing afterpotential of acutely isolated, medium diameter rat dorsal root ganglion neurons.

AIM: Na+-activated K+ (K(Na)) channels set and stabilize resting membrane potential in rat small dorsal root ganglion (DRG) neurons. However, whether K(Na) channels play the same role in other size DRG neurons is still elusive. The aim of this study is to identify the existence and potential physiological functions of K(Na) channels in medium diameter (25-35 microm) DRG neurons. METHODS: Inside-out and whole-cell patch-clamp were used to study the electrophysiological characterizations of native K(Na) channels. RT-PCR was used to identify the existence of Slack and Slick genes. RESULTS: We report that K(Na) channels are required for depolarizing afterpotential (DAP) in medium sized rat DRG neurons. In inside-out patches, K(Na) channels represented 201 pS unitary chord conductance and were activated by cytoplasmic Na+ [the half maximal effective concentration (EC50): 35 mmol/L] in 160 mmol/L symmetrical K+o/K+i solution. Additionally, these K(Na) channels also represented cytoplasmic Cl(-)-dependent activation. RT-PCR confirmed the existence of Slack and Slick genes in DRG neurons. Tetrodotoxin (TTX, 100 nmol/L) completely blocked the DRG inward Na+ currents, and the following outward currents which were thought to be K(Na) currents. The DAP was increased when extracellular Na+ was replaced by Li+. CONCLUSION: We conclude that Slack and Slick K(Na) channels are required for DAP of medium diameter rat DRG neurons that regulate DRG action potential repolarization.

Characterization of voltage-and Ca2+-activated K+ channels in rat dorsal root ganglion neurons.

Auxiliary beta-subunits associated with pore-forming Slo1 alpha-subunits play an essential role in regulating functional properties of large-conductance, voltage- and Ca(2+)-activated K(+) channels commonly termed BK channels. Even though both noninactivating and inactivating BK channels are thought to be regulated by beta-subunits (beta1, beta2, beta3, or beta4), the molecular determinants underlying inactivating BK channels in native cells have not been extensively demonstrated. In this study, rbeta2 (but not rbeta3-subunit) was identified as a molecular component in rat lumbar L4-6 dorsal root ganglia (DRG) by RT-PCR responsible for inactivating large-conductance Ca(2+)-dependent K(+) currents (BK(i) currents) in small sensory neurons. The properties of native BK(i) currents obtained from both whole-cell and inside-out patches are very similar to inactivating BK channels produced by co-expressing mSlo1 alpha- and hbeta2-subunits in Xenopus oocytes. Intracellular application of 0.5 mg/ml trypsin removes inactivation of BK(i) channels, and the specific blockers of BK channels, charybdotoxin (ChTX) and iberiotoxin (IbTX), inhibit these BK(i) currents. Single BK(i) channel currents derived from inside-out patches revealed that one BK(i) channel contained three rbeta2-subunits (on average), with a single-channel conductance about 217 pS under 160 K(+) symmetrical recording conditions. Blockade of BK(i) channels by 100 nM IbTX augmented firing frequency, broadened action potential waveform and reduced after-hyperpolarization. We propose that the BK(i) channels in small diameter DRG sensory neurons might play an important role in regulating nociceptive input to the central nervous system (CNS).

[The effects of burn serum on the erythropoiesis and granulopoiesis in bone marrow in mice].

OBJECTIVE: To observe the effects of burn serum on the erythropoiesis and granulopoiesis in bone marrow in mice, and to explore the possible underlying mechanism. METHODS: Murine bone marrow cell (BMC) strain was prepared routinely and was employed in the establishment of the culture system of colony forming units of erythrocytes, or granulocytes and monocytes. To both sets of culture system normal murine serum (N group) and burn serum, which was collected from the mice with 15% full thickness burn at 12 postburn hours (PBH) and 1, 3, 5, 7 and 10 postburn days (PBD), (burn serum group) was added. In addition, positive control and blank control groups were set accordingly. The stimulating activity of all kinds of sera on the BMCs in the two sets of culture system was determined. The changes in the burn serum concentrations of EPO and GM-CSF were detected by radioimmunoassay, and the data were analyzed by logarithmic linear fitting correlation with the former influence of burn sera on the erythrocytes and granulocytes. RESULTS: (1) Burn sera exhibited obvious stimulation promoting activity on the erythropoiesis and granulopoiesis in BMC, and the activity peaked (384 +/- 60 and 127 +/- 16 CFU) on 1 PBD and decreased thereafter to approach the values found in normal sera group (125 +/- 14 and 34 +/- 20 CFU) on 7 PBD. (2) The EPO content in burn serum was evidently higher than the normal value (P < 0.01) during 12 PBH to 7PBD period. The GM-CSF concentration was obviously higher than the normal value (P < 0.05) at 12 PBH and on 1 PBD. (3) The EPO concentration in burn serum was significantly and logarithmically correlated with the stimulation promoting activity of burn serum on erythropoiesis (r = 0.8570, P = 0.0137). But the GM-CSF concentration in culture with burn serum was not correlated with the stimulation promoting activity of burn serum on granulopoiesis (r = 0.7049, P > 0.05). CONCLUSION: The sera harvested from burned mice during early postburn stage exhibited strong stimulation promoting activity on the erythropoiesis and granulopoiesis in bone marrow. The increased EPO level in burn serum might be the important factor contributing strong stimulation action on erythropoiesis, while increased GM-CSF level was not.