ABSTRACT
BACKGROUND: Small-conductance calcium-activated potassium (SK) channels play an important role in atrial electrophysiology. Blocking SK channels prolongs action potential (AP) duration and attenuate electrical remodelling. The effects of SK blocking on the pulmonary vein (PV) and the sinoatrial node (SAN) remain unclear. MATERIALS AND METHODS: Conventional microelectrodes were used to record the AP in SANs and in isolated rabbit PVs with and without denudation before and after treatment with apamin (1, 10 nM). Using the whole-cell patch-clamp technique, the SK current was investigated in isolated single PV and SAN myocytes. RESULTS: In nondenudated PVs (n = 6), apamin (1 and 10 nM) increased PV spontaneous activity (from 1.8 ± 0.2 Hz to 2.4 ± 0.2 Hz and 2.3 ± 0.2 Hz, P < 0.05) and increased the PV tension by 42 ± 14% and 37 ± 11%. Conversely, in denudated PVs (n = 6), apamin (1 and 10 nM) decreased spontaneous activity (from 2.2 ± 0.3 Hz to 1.9 ± 0.2 Hz and 1.8 ± 0.2 Hz, P < 0.05) and prolonged AP duration without changing PV tensions. Additionally, apamin (1 and 10 nM) decreased spontaneous activity (from 2.8 ± 0.1 Hz to 2.4 ± 0.1 Hz, and 2.4 ± 0.1 Hz, P < 0.05) and prolonged AP duration in SAN (n = 6). SAN myocytes had larger SK currents than did PV cardiomyocytes. Treatment with apamin (10 nM) resulted in a greater decrease (25 ± 8 vs. 20 ± 13%, P < 0.05) in spontaneous activity in isolated single SAN (n = 17) vs. PV cardiomyocytes (n = 16). CONCLUSION: Small-conductance calcium-activated potassium channels play a key role in SAN and PV spontaneous activity and AP morphology. Apamin may modulate PV electrical activity with and without endothelium dependence.
Subject(s)
Apamin/pharmacology , Calcium Channel Blockers/pharmacology , Pulmonary Veins/drug effects , Sinoatrial Node/drug effects , Small-Conductance Calcium-Activated Potassium Channels/antagonists & inhibitors , Action Potentials/drug effects , Animals , Muscle Cells/drug effects , Myocytes, Cardiac/drug effects , RabbitsABSTRACT
Kisspeptin signaling via its cognate receptor G protein-coupled receptor 54 (GPR54) in gonadotropin-releasing hormone (GnRH) neurons plays a critical role in regulating pituitary secretion of luteinizing hormone and thus reproductive function. GPR54 is G(q)-coupled to activation of phospholipase C and multiple second messenger signaling pathways. Previous studies have shown that kisspeptin potently depolarizes GnRH neurons through the activation of canonical transient receptor potential channels and inhibition of inwardly rectifying K(+) channels to generate sustained firing. Since the initial studies showing that kisspeptin has prolonged effects, the question has been why is there very little spike frequency adaption during sustained firing? Presently, we have discovered that kisspeptin reduces spike frequency adaptation and prolongs firing via the inhibition of a calcium-activated slow afterhyperpolarization current (I(sAHP)). GnRH neurons expressed two distinct I(sAHP), a kisspeptin-sensitive and an apamin-sensitive I(sAHP). Essentially, kisspeptin inhibited 50% of the I(sAHP) and apamin inhibited the other 50% of the current. Furthermore, the kisspeptin-mediated inhibition of I(sAHP) was abrogated by the protein kinase C (PKC) inhibitor calphostin C, and the PKC activator phorbol 12,13-dibutyrate mimicked and occluded any further effects of kisspeptin on I(sAHP). The protein kinase A (PKA) inhibitors H-89 and the Rp diastereomer of adenosine 3',5'-cyclic monophosphorothioate had no effect on the kisspeptin-mediated inhibition but were able to abrogate the inhibitory effects of forskolin on the I(sAHP), suggesting that PKA is not involved. Therefore, in addition to increasing the firing rate through an overt depolarization, kisspeptin can also facilitate sustained firing through inhibiting an apamin-insensitive I(sAHP) in GnRH neurons via a PKC.
Subject(s)
Action Potentials/drug effects , Gonadotropin-Releasing Hormone/metabolism , Kisspeptins/pharmacology , Neurons/drug effects , Protein Kinase C/metabolism , Action Potentials/physiology , Animals , Calcium/metabolism , Female , Membrane Potentials/drug effects , Membrane Potentials/physiology , Mice , Neurons/physiology , Patch-Clamp Techniques , Signal Transduction/drug effectsABSTRACT
AIM To clarify the mechanism of berberine on mobility diarrhea by investigating the effects of berberine on calcium-activated potassium current I K(Ca) and delayed-rectifier potassium channel current I K(V) of guinea pig colonic smooth muscle cells. METHODS Single guinea pig colonic smooth muscle cells was isolated by collagenase; The effects of berberine on I K(Ca) and I K(V) were detected by using patch clamp technique, under the conventional whole cell patch clamp mode. RESULTS 10, 50, 100 ?mol?L -1 berberine inhibited I K(Ca) of guinea pig colonic smooth muscle cells significantly (P
